The pursuit of happiness is something we all share as a Declaration of Independence promise, but the mere existence of cars such as these makes it clear that some of us are inclined to pursue happiness more rapidly than others. In fact, for some there's a direct correlation between the velocity of the pursuit and the level of happiness. The framers of the Declaration couldn't foresee how far this phenomenon would go, but they can be forgiven, toiling, as they were, a long time before the establishment of Audi, BMW, Jaguar, and Mercedes-Benz.

Would Thomas Jefferson have idealized an America of self-sufficient yeoman farmers if he'd known that someday there would be a Mercedes E55 AMG? Not likely. For one thing, a device such as this blitzin' Benz is clearly beyond the economic horizon of simple yeoman farmers. For another, T.J. would have been kicking himself for having been born a couple centuries too early. Even a guy who'd never seen an automobile could appreciate these formidable four-doors.

For the driver who wants sports-car performance with luxo-sedan convenience and comfort, it doesn't get any better than this. It can get fancier, it can entail even more power, and it can get a whole lot more expensive. But not better, when better is defined as quicker and more agile.

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We need to temper the foregoing. Although they're all fast, with two-ton curb weights no player in this quartet has the moves of a BMW M3. On the other hand, they're close to that standard (the handling guys seem to keep finding ways to enlarge the loopholes in the laws of physics), and beyond this size-and-performance class the offerings become more relaxed in character and even heavier.

They also become triple-digit dear. Go beyond the Audi RS 6, and you're in the realm of cars with hacienda-size price tags. For that matter, the window stickers of our test group aren't for the faint of pocket. The demographers tell us these formidable four-doors are likely to attract mostly guys (90 percent, according to Audi), mostly in the 45-to-50 age range, mostly making upwards of 250 large. Guys whose pockets are, if not Maybach bottomless, at least deep enough to indulge in lavish whims.

So before lighting the fuses, we spent some time speculating on what sort of driving priorities these guys might bring to the showroom. Would they want relentless rush? Speed is a common denominator here, but it's clear that some members of this classy cartel deliver more of it than others. Leather-clad hedonism augmented by symphonic sound systems? Another common denominator, but with only subtle variations. How about halfback agility? Significant distinctions on that front, for sure, but significant divisions within the test crew on its importance. And 600 miles of touring blitz amid the exotic cactus-clad landscape of southern Arizona didn't entirely resolve those divisions.

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We were unanimous on one point, though. These sedans are seductive in the extreme—stylish, handsomely appointed, competent, and, as noted, capable of shrinking distances in a faster-than-average hurry. Much faster. Beyond that, the distinctions get to be pretty subjective.

You may recall we've visited this category before ("Battle of the Best," March 2000). In that test, the then-new M5 squared off against a Jaguar XJR and a Mercedes E55 AMG.

How quickly things change. The M5 goes from youthful phenom to seasoned veteran, facing fresh challengers from Audi, Jaguar, and Mercedes, and the horsepower standards have escalated by a bunch. Three years ago the Bimmer's 4.9-liter DOHC 32-valve V-8 made it the power player of the supersedan pack. This time around, the same car comes to the starting grid with the second-lowest horsepower rating (394 versus the Jag's 390) and the lowest torque numbers. The E55 AMG, meanwhile, has been made over and enters the fray with eye-widening output from its supercharged 5.4-liter V-8—469 horsepower and 516 pound-feet of torque, a huge uptick from the 349 horsepower and 391 pound-feet of its naturally aspirated predecessor. Audi's entry is only slightly less potent. Clearly, the ante has gone up in this thoroughbred sweepstakes. So, who holds the winning ticket now? Only one way to find out.

The numbers tell much of the story here. Our arrest-me-red S-type R sprinted to 60 mph in 5.4 seconds and cruised through the quarter-mile in 13.8 seconds at 103 mph—pretty much what Jaguar forecasts for this car. These results don't exactly fall into the realm of somnambulism, but in this group they do fall into the also-ran category.

How important is that to you? If the answer is "not very," then you're the guy Jaguar's product development people had in mind when they penciled in this car's persona. The idea, according to Jaguar, was to create a refined four-door that would pack enough power to set it apart from the more mundane luxo-sports-sedan offerings of, say, Lexus, Infiniti, and Cadillac.

They most emphatically did not set out, they will tell you, to create a head-on challenger to the BMW M5.

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We'd say the development team hit its target. The S-type R eschews the gunfighter reflexes of a hard-edged supersedan such as the M5 in favor of a smoother ride, elevated elegance, and a more laid-back approach to fast touring.

How the team got there, though, is a little mystifying. A key point of distinction between the S-type R and the S-type 4.2 is an Eaton supercharger force-feeding the intake system of the 4.2-liter DOHC 32-valve aluminum V-8. Running at max boost—13.1 psi—the blower bumps output from the naturally aspirated engine's 294 horsepower and 303 pound-feet of torque to 390 horsepower and 399 pound-feet.

Those are fairly robust numbers, but having achieved the extra grunt, the engineers seemingly set out to make sure the engine couldn't feed all that power into the drivetrain in big, hard-to-digest lumps. The engine-control program upshifts a little short of the 6250-rpm power peak, particularly in the lower gears, and the shifts are heavily damped—mustn't have lumpy shifting, y'know. And even though the six-speed automatic is exemplary in its smooth operation, it's no ally of haste, controlled, as it is, through Jaguar's traditional J-gate shifter. So the R's specifications are belied by its straight-ahead performance.

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The Jag's handling is similarly constrained, but here the distinction is more subtle. Although tuned for supple ride quality, the S-type R hasn't entirely abandoned the art of transient response. It surprised us with the best lane-change time, despite developing the least grip on the skidpad, and it was willing—if not always able—to keep up on serpentine byways. Braking was also respectable, on a par with all but the BMW at the test track, although there were reports of mild fade on mountain roads.

If the Jag wasn't always up to the pace of the rest of the pack, it got solid marks in other categories. Its handsome interior was the only one to offer a real color scheme, its passing performance was brisk, and the refined whine of its supercharger made drivers look for reasons to tromp on the gas.

Most enticing of all, the Jag delivers its muted supersedan message for some 10 grand less than anything else in this showdown. If absolute haste isn't an issue, that price makes the S-type R hard to ignore.

Three years ago, the E55 was outpaced by the M5 in every standing-start acceleration category, as well as the lane-change test and Nelson Ledges racetrack lap times. The E55 had to plead no contest.

Flash forward to '03: an all-new E-class, which prevailed in our most recent comparison of mid-lux sedans ("The Magnificent Not-Quites," March 2003) and an all-new AMG derivative. No danger of playing second fiddle to the BMW in the sprints this time.

Propelled by the same supercharged 5.4-liter SOHC 24-valve V-8 employed in the SL55 AMG, albeit with a little less horsepower, it's even faster than the SL55 we tested last November, clocking 0 to 60 in 4.3 seconds, 0 to 100 in 9.9, 0 to 150 in 24.5, and the quarter in 12.5 seconds at 116 mph. That's quicker than anything else in this roundup—quicker, in fact, than any production sedan we've ever tested. Sports-car quick. The last Corvette Z06 we tested (December 2001) hit 60 mph in 4.0 seconds, 100 in 9.2, and 150 in 24.1, and it covered the quarter in 12.4 seconds at 116 mph.

The E55's torque reserves seem bottomless, peaking at just 2650 rpm and staying there until shortly after noon. An electromagnetic clutch reduces supercharger parasitic losses when the driver isn't calling for max thrust, but tromp that pedal at almost any speed, and the Benz squashes its occupants into the beautifully contoured seatbacks.

Clearly, this is a much different animal than its predecessor. Ride quality hasn't suffered much, thanks to the three-way-adjustable Airmatic DC suspension, but the seductive omnipresence of so much brute force gives the new Benz a bad-boy dimension that was previously absent.

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Still, as irresistible as it is as a highway missile, the E55 had just enough quirks to leave it one point behind the BMW in the voting. There's the issue of mass. At 4237 pounds, the E55 was the porker of this foursome, heavier than the all-wheel-drive RS 6 and 472 pounds heavier than the previous E55. The extra bulk didn't hamper its straight-ahead prowess, but it was a handicap in quick directional changes, and it didn't help in the braking department, either. Despite eight-piston calipers gripping each king-size front rotor, the Benz needed 173 feet to stop from 70 mph, fourth best of four and 12 more feet than the Y2K E55.

There was another brake issue, one we've noted before. The Mercedes brake-assist program makes it just flat impossible to be smooth with the binders, particularly at higher speeds. It never sleeps, and the result is a lot of lurch and lunge as the system reads the driver's activities and applies its own interpretation of what the brakes should be doing.

The steering-assist program is similar, changing effort from near zero to heavy in a blink without delivering a corresponding increase in feel. That can be disconcerting in a car that gets a little frisky at the limits of its substantial adhesion. With all the stability-control enhancements switched off, the E55 was more willing to wag its tail than the others, accounting for its last-place performance in the lane change. In high-speed corners and fast transitions, both the BMW and the Audi inspired more confidence.

"Finesse isn't really part of its game," wrote one tester.

Still, the E55's visceral appeal is undeniable, and with its load of standard luxury features, it's a good value. For the guy who wants the fastest four-door on the block, the Benz simply can't be beat, for any money.

In 2000, we called this car "the most desirable sedan in the world," something that's still pretty much true today. Pretty much.

Make no mistake, on a stretch of winding road with lots of low-speed switchbacks, the M5 is still the most athletic player in this quartet. Although it's only slightly lighter than its rivals, less is more when it comes to quick maneuvers, and the M5's modestly lower mass is augmented by the best weight distribution in the group—52.2/47.8 percent, front to rear. It all adds up to a two-tonner that doesn't mind being tossed around a bit, provided the stability control is switched off beforehand. When that system is active, it intervenes at the first hint of a slide, and it intervenes emphatically. The same electronic overreaction is programmed into the E55's systems, and in contrast to Audi's high-threshold approach, we think it's overdone, like a mother snatching her child back from the brink of a chasm when in fact he's standing on a curb. Lighten up, dudes.

Another area where the M5 continues to hold an edge over its challengers is in braking. All four of these cars have powerful brake systems—big vented front rotors squeezed by multipiston calipers—with anti-lock brakes standard—but the M5 turned in the best stopping distance from 70 mph, the only car under 170 feet. Pedal feel was excellent, and fade was a non-factor, even in hard mountain driving.

And of course the Bimmer was the only supersedan equipped with a manual transmission. Automatics are swell in urban traffic, and some offer a pretty good approximation of manual control—the E55's five-speed is a good example. But there is still nothing to rival the sense of involvement that goes with shifting for yourself, and the M5's six-speed does an excellent job of keeping the 4.9-liter V-8 in the sweet part of its power band.

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Staying in the heart of the power band was more important for the M5 this time around than three years ago, when it was hard to imagine 400 horsepower might not be enough. But that was the case in this encounter. The Bimmer was third to 60 mph at 4.9 seconds and third in the quarter-mile, 13.4 seconds at 108 mph. And even though the M5 began to gain on the Audi when speeds crept above 130 mph, it couldn't touch the Benz. Just as in the old "Hot Rod Lincoln" rockabilly tune, "by then the taillight was all you could see."

Besides the M5's power disparity—remember, we're talking relativity here—there were a few other niggles. For example, although we preferred the BMW's manual transmission (the only gearbox offered) to any of the automatics, there were logbook comments criticizing its overly long shift throws and slow engagements. The M5's body roll also drew some carping, and the recirculating-ball steering had a bit too much power assist for optimal feel.

Inside, the M5's dashboard is dated, the upper portion of the major gauges can be obscured by the bridge-cable wheel rim in certain driving positions, and its rear seat measures up as a bit confined versus that in the roomier RS 6.

Do you perceive a serious shortfall in the foregoing? Neither did we, really. With its understated muscularity and sweet lines, the M5 is still a handsome piece, even though the current 5-series is now seven years old and counting down to a major makeover for 2004. Just as important, the M5 also continues to be a treat for the driver who wants his luxury augmented by mega-performance.

But it's no longer the outright champ of the supersedan decathlon.

One of the time-honored rationales for corporate motorsports programs is technology transfer, in which systems developed and tested in racing cars find their way into street models. Thus, Audi presents the RS 6 as a legacy of the all-conquering R8 racers, winners of the 24-hour Le Mans race in 2000, '01, and '02. That's a stretch. Aside from its turbo V-8, the RS 6 has as much in common with the R8 as it does with the Graf Zeppelin. But if that's Audi's story, it's okay with us, because the RS 6 goes way beyond okay.

We should also acknowledge where it doesn't go: It doesn't go faster than the E55. With twin turbos and intercoolers, this is the most potent iteration of Audi's 4.2-liter DOHC 40-valve V-8—450 horsepower, 415 pound-feet of torque. The torque is particularly impressive. It's all on tap by 1950 rpm—barely off idle—and it continues at peak output all the way to 5700 rpm, a curve similar to the topography of southeast Michigan, i.e., broad and flat.

Instant torque and all-wheel drive conspire to hammer this big car to 60 mph in 4.4 seconds, just a 10th shy of the bodacious Benz, and its departure is remarkably free of drama. The small-block-Chevy rap of its twin exhausts— delightfully brash in a car of this caliber—climbs the decibel scale, the RS 6 hunkers down on its haunches, and suddenly, it's gone, diminishing rapidly into the Arizona sunset. The speedo hits 100 mph in 10.7 seconds, and the quarter-mile comes up in 12.8 seconds at 108 mph.

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Impressive numbers, but still, they pale a little next to the heady rush of the E55.

The RS 6 was no gazelle in tight turns and transitions. Its mass—just eight pounds lighter than the Benz—was a handicap, as was its worst-in-group weight distribution, 59.6/40.4, a function of its front-drive-sedan derivation and engine location. With almost all the V-8's mass hung out beyond the front-axle center line, low-speed understeer is hard to avoid.

On the other hand, put the RS 6 on a back road with lots of fast sweepers—Tucson's Mt. Lemmon, for example, soaring from low desert to more than 8000 feet—and it is very, very hard to catch. The combination of all-wheel drive and Y-rated 255/40R-18 Pirelli P Zero Rossos pulled 0.87 g on the skidpad—the best grip in the group. Audi's Dynamic Ride Control (DRC), a refreshingly mechanical (as distinct from computer-controlled) hydraulic system, transfers shock-absorber oil between the diagonal corners to reduce body roll, dive, and squat, keeping the RS 6 level as it carves its way through canyons—with no apparent compromise in ride quality.

Flat cornering, plus Super Glue adhesion, plus beautifully weighted steering, plus abundant power, plus monster brakes—the front calipers grip with eight pistons—make the RS 6 a supremely composed performer at high speeds. It inspires confidence that goes beyond its rivals'—an endearing trait in a car in this performance category.

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There are some soft points. In urban traffic the RS 6 will lunge a bit at launch, the manumatic function of the five-speed automatic tended to upshift without orders, and some—though not all—testers remarked on turbo lag.

Then there was the issue of price. At this writing, Audi sources were only willing to say "less than $85,000," although we've also heard an estimate of $82,000. Considering what the competition is offering for about $10,000 less, either number is pretty tough to swallow. Nevertheless, the RS 6's blend of power, high-speed aplomb, comfort, and superb workmanship carries the day.

A logbook entry summed up our collective reaction: "So stable, so potent, such brakes, such comfort. Wow." The wows have it.

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