Some serious model proliferation has been going on at Mercedes-AMG, and few enthusiasts will have a problem with that. What began a couple of years ago as a follow-up to the gullwing-door SLS has grown into a model line unto itself. The AMG GT is now seven models, including the base GT, the GT S, the GT R, the GT3 race car, the GT convertible, the GT C roadster, and the GT C coupe. There will shortly be a long-rumored four-door GT variant making the grand GT total eight. Let there be no doubt that the upper end of the sports car market is alive and kicking.

The latest version we test drove, the GT C roadster, is packed with power and attitude, and it loses nothing in the transition from closed-top coupe to open-top hedonist. From C coupe to C roadster, weight is up a mere 75 pounds (34 kg)—a rounding error in the grand scheme of 3,800-pound (1,724-kg) things. Additional fortification goes into the door sills, rear bracing between the wheel housings, the rear bulkhead, and up front, hidden beneath the dashboard.

Hand-built engines, hand-coded suspension

Inside, the roadster feels spacious, even if there isn't really much more room than in the Jaguar F-Type . Overall width and a wide transmission tunnel will do that for you. Only when the soft top is up will you notice any compromise from the GT coupe; the roadster does make you feel a bit hemmed in up around your head space. Top down, everything improves, and the fact that the top lowers in a scant 11 seconds while the car is traveling at up to 31 mph (50 km/h) is a bonus. The AMG GT C also offers an AMG Track Pace iPhone app, which keeps lap times when at the track. It can record video, too.

Basic drivetrain layout is the same as the other AMG GT models, centered around a front-mid mounted 4.0L twin-turbo V8 connected to a rear-mounted dual-clutch transaxle with seven speeds. Non-C models churn out 469hp (350kW) and 465lb-ft (630Nm) of torque, while the Cs bump those figures to 550hp (410kW) and 502lb-ft (681Nm).

But the more interesting bits are hidden from view. Both C models have wider rear fenders, a rear track that's wider by 2.2 inches (56mm), a rear-steer system which dials up out-of-phase steering angle at speeds below 62mph (100km/h), and same-phase angle at higher speeds and an electronic limited-slip differential. The Cs also have the R model's variable-stiffness engine and transmission mounts. During aggressive driving, they firm up, and when easy-going, they soften.

Multiple driving modes—Comfort, Sport, Sport +, and Race, the latter on the C models only—adjust damping and throttle response. Through desert-canyon twisties that varied widely in speed from 30-90mph (48-145km/h), the GT C roadster responded, handled, and gripped like no car as wide, except perhaps a Viper.

That comparison is apt. The C's super-long hood, big engine, huge torque, and rear-biased driving position echo the Viper and its traditional layout. So did the predecessor SLS and even the old, (highly compromised) Mercedes-McLaren SLR. But that sizable feel to the GT C roadster seems to shrink the faster you go, or, at a minimum, it just doesn't register as much as does the cornering speeds the car can achieve with little effort. And the brakes are up to everything the engine and suspension can dish out, using 15.4-inch (391mm) front and 14.2-inch (361mm) rear vented and perforated discs, with carbon ceramic discs optional.

Grip level is astounding. Braking performance is astounding. Oomph coming off of corners is astounding. In a straight line, the C should reach 60mph (97kph) in about 3.0 seconds, or 0.2 quicker than the non-C models, which, no matter how you slice it is Quick with a capital "Q."

A roadster to rival the supercar?

Add up both the hard numbers and the softer feelings when driving it, and the AMG GT C becomes a strong foil to more high-strung exotica. I'd venture to guess that dynamically, few owners will ever approach the GT C's capability, which is a bit of a shame because, driven well, the GT C could show a taillight or two to even more expensive machinery.

The biggest downside is luggage space, or lack thereof. You will not fit large- or even medium-sized luggage in the GT C's trunk, and there's no place for anything beyond a briefcase inside the cabin. And while you can't deny the twin-turbo V8's stonking torque and power, it sounds a bit ruffian and big-block Yank-ish, especially considering the sophistication of the chassis that greets you when the road starts getting curvy. (However, some of us quite like the noise of a raucous AMG V8—Ed.)

Due to dealers this fall, the GT and GT C roadsters will likely span the bridge between $130,000 and $160,000—a bridge that will take no time to cross.

Listing image by Mercedes-Benz