As a class, I suppose you could call both the SRT Viper GTS and Mercedes-Benz SLS AMG GT the "what if" cars.

In 1988, Bob Lutz said to Chrysler designers (in so many words): "What if we could build a brutal, basic, no-nonsense sports car along the lines of a

427 Cobra but give it thoroughly modern brakes and suspension and a great, big, honking aluminum engine with fuel injection?"

And at Mercedes, about eight years later, you can imagine them saying (in German, of course): "Perhaps our most beautiful and charismatic sports car

ever was the 300SL. What if we did a modern version, working with our corporate Viper brethren at Dodge, using everything we've learned in the last 70

years about suspension, chassis stiffness, and engines?"

And those questions were answered with the two cars we have here. That they both exist in the year 2013 is nothing short of a miracle. If you'd told me

during the first great fuel crisis of 1973 that, 40 years later, the auto industry would be producing cars like the 640-hp Viper GTS and 583-hp SLS,

you'd have been answered with the drooling, incoherent stare of a medieval peasant being told about the Saturn V moon rocket.

Yet after a two-year hiatus (time out for national and corporate financial healing) the Fiat-approved Viper line is revamped and running again on

Conner Avenue in Detroit, turning out cars under the SRT rather than Dodge banner, now with 40 more horses and an upgraded cabin intended to compare

with top imports. As first conceived, the Viper was intended to be, almost literally, a "blast" to drive, with all the explosiveness and brevity that

word implies. But the new version is meant to be a more sustainable daily driver and road car for longer trips—without losing any of its warrior

personality. Sort of a Darth Vader with voice lessons.

Does it succeed? To find out, we took it on a California mountain road trip (with some freeways) in the company of a red Mercedes SLS AMG GT coupe. The

SLS has plenty of its own big-block brutality to offer in the form of that crazed 6.2-liter V8, but Mercedes has always dressed it in the most elegant

straitjacket it could devise, including a seven-speed dual-clutch automatic transaxle with paddle shifters (the Viper comes with a six-speed manual

gearbox), more sound deadening, and a generally more luxurious interior. There's a cost to this coddling, of course: At 3760 pounds, the SLS, even with

its all-aluminum frame, is 380 pounds heavier than the Viper. And it's much more expensive. As equipped for this road test, with their various track

packages, sound systems, fine leather, etc., the true window stickers for the SLS and Viper were $231,605 and $142,990, respectively.

With all that in mind, we hit California's Pacific Coast Highway and from there headed up through the fast and endless canyon curves of California

State Route 33 over the Coast Range toward Buttonwillow Raceway. Intrepid Road Test Editor Robin Warner and I traded cars several times and repeated a

few sections of good road for back-to-back comparisons.

I started out by lifting the famous gullwing door of the SLS, sliding in over the great vastness of the doorsill and tucking my legs into the footwell.

This is not a vehicle your UPS driver would want to hop in and out of all day. Even with my long simian arms, I was just able to lower the door, a

rotator-cuff challenge that would tempt me to hang a small leather strap on the handle.

Warning: Mr. Warner and I both clouted our heads several times getting into or out of the SLS, especially when we ducked back into the car to retrieve

something and forgot the door was hovering overhead. I suspect, like a rat in the world's fastest Skinner box, you learn. You also learn to exit the

car like a person leaving a helicopter, ducking under the rotor blades until clear.

So yes, the doors are something of a nuisance, but would we change them? Never. They're an important part of the car's beauty and mystique. Get over

it, as mom used to say.

When you hit the starter button on the Mercedes, it fires up with a satisfying crackle and growl, deep and leonine. Select D and you're off. The car is

effortlessly quick and smooth on the freeways, and when you turn onto the mountain roads, the steering is linear, with just the right amount of

feedback, while the extraordinarily firm suspension allows minimal body roll. Tire grip is far beyond sane human limits on a public highway, and the

brakes are extremely powerful without being consciously hard to modulate.

It feels like a big, solid chunk of car when you're hustling it through the curves, but it is balanced and easy to drive.

Enter the Viper. A little leg folding required, but less than in the SLS. The new leather Sabelt seats are arguably no better than those in the

last-generation Viper, but they recline farther than those in the SLS—better for tall people like me who drive in the "space launch" position. I found

the nontelescoping wheel a little close, however, until I used the handy electronic pedal-cluster adjustment to get comfortable. The low double-bubble

roofline makes the windshield seem bunkerlike, but the view over the rounded forms of the carbon-fiber hood and aluminum fenders is very pretty.

That big 8.4-liter V10 engine barks to life with a more guttural, ripping sound than the SLS's V8. Louder on the road, too, as is wind noise, so

there's more of a dull booming roar in the Viper's cockpit than in the serene Mercedes. I found the precise, tightly spaced Tremec six-speed and the

medium-to-heavy clutch just right for my own tastes, though Warner reported that the clutch induced a bit of soreness in stop-and-go traffic.

In the mountains, I immediately warmed up to the Viper because it seems smaller and more compact than the SLS—which it is, with a 6.7-inch-shorter

wheelbase and 6.9 inches less in the way of length—so it feels shorter-coupled and more tossable. The Mercedes does everything flawlessly but gives you

a sense of sitting in a larger, grander car that's taking you for a ride. The Viper has a more personal, direct feel, almost (dare I say it) like a

large, heavy-duty Miata with a monster engine up front and the driver way, way in back. Steering is quicker—almost too quick initially, as you find

yourself turning in and then having to back off a notch until you're used to it—so you do more sawing at the wheel. The Viper keeps you busier, but I

found it more visceral and fun to drive on narrow, twisting roads, a pure unvarnished sports car to the SLS's more graceful GT personality.

Strangely, that hyperactivity also applies to the Viper's huge engine. Despite its massive 600 lb-ft torque rating, the V10 has to be worked harder than

you'd expect to run with the lazy-fast Mercedes. Some of this may just be very tall gears in the manual 'box, but some is no doubt from the relatively high

rpm torque peak. Step out of the Viper and into the SLS, and you might suspect the Mercedes of having the larger engine. Both cars are tremendously quick,

but the SLS's drivetrain seems to read your mind, holding gears between corners and hooking up instantly at any speed to fling the car down the road with

scenery-blurring ease.

The racetrack, however, was not so easily swayed by these subjective impressions. With Editor-in-Chief Larry Webster at the wheel, the Viper hot-lapped

Buttonwillow a good 1.43 seconds quicker than the SLS and did the 0-to-60 sprint in 3.5 instead of 3.7 seconds. He did his best times with the stability

control off in both cars, as is usual, and said the SLS requires that you keep your wits about you and the rear end under control with the throttle. The

Viper was easier to drive (steering busyness aside) because the rear end didn't want to drift to the same insane degree, but it was not as much fun. Almost

the reverse of our road impressions.

Of course, similarities aside, no one cross-shops these mechanical asylum escapees. Which one you pick would probably boil down to highly personal

considerations of price, aesthetics, history, and what kind of driving you plan to do. Put those all in the blender, however, and my own favorite margarita

would be the Viper. It's more of a basic sports car and short-distance canyon blaster, but also perhaps a little more nimble as a daily driver and

errand-runner, thanks partly to its conventional doors. I also like its smaller apparent size—it's only seven inches shorter, but it seems like more—and

would probably drive it more often. And then there's the price. The Viper's new cloak of civility really does push it over the edge into the real world of

driving (just), without compromising its tough-guy reputation.

That said, the SLS would be an easy first choice for a long road trip. It's simply quieter, smoother, and less tiring. The same undertone of brutality is

there but buried just a little further beneath the surface. Beyond that, the Mercedes is stunning to look at and beautifully crafted.

And it has those gullwing doors.

Whatever the truth may be behind their origins, whatever their theoretical similarities, these cars are both "ruthless and majestic," as Ian Fleming once

said of the original 300SL. And each is a perfectly modern study in the traditional virtues and colorful disadvantages for which we romantics will pay good

money.

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