KANAB, UTAH—It's a perfect autumn driving day, crisp and clear and just warm enough to put the top down. I'm blasting through the country's most spectacular scenery in one of history's most spectacular cars, a 1958 Mercedes 300 SL roadster. The speedo is wavering just past 100, and although the tachometer has been disconnected—the cable was squealing in the cold—I know from the engine's wail that we're around 4,500 rpm.

There's a curve up ahead, so I squeeze the drum brakes and drop down to 60. Just for giggles I try for—and get—a perfect double-clutch matched-rev downshift into third. I yank hard on the wheel, then I'm back on the accelerator, up to 80, and up into top gear. The engine's deep roar is like no other six I've ever heard, but it sounds best above 4,000 rpm and I'm determined to keep it there.

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I'm also doing my best to forget that I'm driving a 35,000-mile original worth around $1.4 million.

"This car feels like you could hammer on it all day," says my co-driver, Michael Kunz, raising his voice above the rushing wind and howling engine.

"We have been hammering on it all day," I yell back. "We've been hammering on it all week." And it's true—we've been driving the 300 SL like college students in a clapped-out Miata, and the car can't seem to get enough.

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Mike is the head of the Mercedes-Benz Classic Center in Irvine, California, which owns the car, and I'm his guest at the second annual Mercedes 300 SL Classic Rally, a gathering of Gullwings and Roadsters on a five-day tour through Utah and Arizona. Technically I'm Mike's co-driver, not the other way around, but he's been unexpectedly generous in sharing the driver's seat. By the end of the rally I will have driven the majority of our 1,300-plus miles.

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I've come because I want to learn more about the enduring appeal of these cars—and because if someone offers you a week in a 300 SL, you'd have to be psychotic to say no.

We all know the 300 SL is a design classic. "The car is exquisite," said David Duthu, a member of the Rally's Board of Directors and owner of a beautiful blue early-production '54 Gullwing, VIN# 016. "From the back, from the front, from the side. The details—everything about it is beautifully designed. But yet every little nuance is there for a reason, and that makes it a better performing car."

That, I am to learn, is a key element in the 300 SL appeal. We've all seen seven-figure classics, but how often do you see forty of them being driven hell-for-leather across the cold desert?

One owner of a '55 coupe who, like a handful of Gullwingers I talked with, prefers to keep a low profile—we'll call him Bob Smith—summed up the appeal: "It's modern-car fast—handling and everything." Indeed, that is the 300 SL's biggest surprise. I expected sloppy 1950s steering, but the 300 SL tracks fairly straight, wandering only slightly at higher speeds. You have to coax it, but you don't have to command it. Duthu mentioned letting go of the wheel to take off his glasses and wipe his eyes—at 120 mph. "I've only done that in a Bugatti Veyron," he says. "That'll give you an idea of how stable it is."

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Turns are another story: The non-assisted steering loads up after only a few degrees of lock. Tight twisties require biceps of iron and thumbs hooked securely in the crossbars, and if the turn radius tightens, it can be a real challenge to keep your line. After the curviest day of driving, several owners complained of sore arms.

"Once it takes a set, you're free to nail the throttle," Kunz advised me. "In fact, you'll want to keep some power on to keep the rear end planted, especially if we're low on fuel. The tank is right on the rear axle, and a Roadster with an empty tank is a very different car than one with a full tank. If it gets light, get your foot into it. Initially the car is a bit intimidating, but then you learn its virtues, and it won't necessarily bite back if you know what you're doing."

Most of the owners I will meet on this trip have had plenty of time to get to know their 300 SLs. "I've had my car 16 years, and I'm a babe in the woods," says Smith. "Another guy here, he got his in '73, another got his in '65. A neighbor of mine bought his in '57 when it was two years old. You go to the Gullwing Group, and most of these guys have had their cars for 30-plus years. After 20, 25 years, maybe it becomes yours instead of, 'Oh, yeah, you have Joe's old car. '"

"A lot of the owners have owned the cars for many generations," Kunz told me. "All of them consider the car to be a blue chip car, not only in terms of dollars but in terms of the experience of owing and using it. That's really what it's all about. They enjoy the cars."

"A 300 SL motor is bulletproof," says Duthu. "As a guy that's owned a lot of Jaguars and Maseratis, [they have] constant problems. This car, I can let it sit a year, go out there and crank it up in two seconds, then get out on the road and never worry about it." Smith agrees: "I thought nothing of hopping in my car and going a thousand miles this week. I'm not worried at all."

Ron Swartz and his wife Ellen Johnson have put over 30,000 miles on their white 1957 Roadster since they bought it in 2003. "We've driven to conventions every year," says Ellen. "East coast, west coast, across the desert."

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"Canada in the snow," Ron adds. "We haven't broken down. Amazing for a car that old."

The Mercedes-Benz Classic Center provides mechanical support for the rally, but Nate Lander, the Center's workshop manager, feels like the Maytag repairman. "Always bored!" he says. What few failures they see, Lander says, "come from people trying to re-engineer the car. They say, 'I drive the car.' Well, they drove the car in 1957, too. The engineers were very, very smart. We try to put it back exactly like it was in 1955 or '57."

The 300 SL's legendary reliability draws flack at multi-marque rallies. "Sometimes the organizers complain that everyone wants to bring a 300 SL," says Kunz. "Well, for good reason. They're easy to deal with, and they won't give you any trouble. They're comfortable, they're capable, you can go pretty hard on the car and the car loves it."

The 300 SL's reputation for dependability is all the more amazing when you consider that it is, quite literally, a racing car modified for street use.

"Mercedes after World War II was in shambles," Smith explains. "They spent a lot of money and came out with this high-end 300 series sedan with a great big heavy cast-iron straight six. And they decided to go back to racing, which they dominated with Auto Union prior to the war. They didn't have the money, but they had this big, heavy engine, and they said, 'OK, let's go racing with that.' The entire car is designed as a solution for this big, heavy engine."

The W194 racer was an immediate success, with several major victories including the 1952 24 Hours of Le Mans. But what attracted most of the attention was the coupe's unusual doors.

"They had to make everything else light, so they designed a [lightweight] space frame," Smith explains. "In order to have the box section they needed they couldn't use a regular door." The solution was the coupe's famous gull wings. "Nobody said the doors had to open from the front. The doors were a solution to keep the weight as light as possible."

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Kunz explained that the production version was very much an American phenomenon. "The importer for the United States, Max Hoffman, convinced the Board of Management to build a road-going version. Had it not been for Max, we probably would not have produced such a car, because they really didn't feel the public would buy it. But he said, 'If you build it, they will buy it,' and he was absolutely correct."

"If you have an all-out Ferrari race car, things can be very delicate," Lander says. "Very thin aluminum sheetmetal. [On the 300 SL], the front axle, rear axle, transmission and even the engine to a lesser extent [are] all standard 300 Sedan and Coupe-Cabriolet parts. This was designed so that a guy or gal off the street could go into a dealership and buy the fastest car in the world and drive it and go get groceries with it. That was a very unusual thing. A lot of people say this is the first supercar, and in a way it is, just because of its exclusivity, its uniqueness. It looked like a space ship in 1954. But it's also very usable."

"It's almost unfair to call it a supercar," Kunz adds, "because what we call a supercar today is not a car you would take for a normal drive. It's totally impractical. This is an all-around car."

When the 300 SL coupe appeared in 1954, it had one very notable upgrade over the W194. While the racing car had carburetors, the production car had fuel injection, increasing output from 175 to 240 hp. The system injected fuel directly into the cylinders, much like a modern car, but without electronics. "It's a little mechanical computer brain," Lander says.

It's also key to the 300 SL's drivability. On our rally, most of the 300 SLs started easily after 20-degree overnight cold soaks and had no problem with the altitude changes. Smith says, "When I take my Allard on the Colorado Grand, I re-jet the carburetor. This, I could drive it from sea level to the top of Pike's Peak and it wouldn't make any difference, because the diaphragm adjusts for atmospheric pressure."

By week's end our 35,000-mile original Roadster is now a 36,000-mile original, and aside from a bit of grease on the wheels—weeping hub bearings—it shows no adverse effects from its five-day caning. It pains me to know that I may never again get to drive so aggressively in something so old and so valuable, but I am grateful to have lived a week in the life of someone who owns one of these magical cars.

"To me, the Mercedes 300 SL is a balance between design and function," Duthu says. "The unique nature of the car, the history, the durability, everything about it. It's like the Beatles. They had number-one albums in three different genres of music. This car bridges the gap across a spectrum of cars. It's a near-perfect package. It's pretty close to being the perfect car."