Its rigid structure contributes to its smooth, quiet operation, lack of vibration, and balance of ride quality and handling capability. A rigid chassis does not mean a stiff ride, however.

The CLK suspension absorbs bumps without fanfare. The only disturbance comes from the crack of tires over potholes, and it's heard more than felt. The CLK is comfortable, but not numbing, so the steering feeds good information back to the driver about how well the front tires are gripping.

This balance of smoothness and road feel means you might be driving the CLK harder than you realize in fairly short order. When the straight, flat roads of the city give way to twisty two-lanes in the hills and countryside, the coupe handles curves with the grace of a thoroughbred. It maintains a nice, flat attitude through sweeping bends and won't bob or weave with frequent application of the brakes.

We like the way Mercedes has refined its electronic stability program, which can help the driver maintain control by reducing skidding. In the CLK, the system is virtually transparent, intervening unobtrusively to prevent wheel spin, but without the heavy-handed reduction in power that marred some of its early applications.

Engine performance is satisfying in all models. The 268-hp V6 in the CLK350 has all the power most drivers need, accelerating with authority from a stoplight and moving the car smoothly through the gears. Acceleration times for the V6 match those for the typical V8-powered luxury car of the late 1990s, and there's a reserve of power that makes passing on two-lane roads a stress-free process.

Nonetheless, the new 5.5-liter V8 in the CLK550 is a significant, noticeable step up, from both the CLK350 and the previous CLK500 models. With 382 horsepower and nearly 400 pound-feet of torque, acceleration here is thrilling. Capable of accelerating from 0 to 60 mph in just 5.1 seconds, the CLK550 is high performance by nearly any definition. Slam the accelerator at any speed and what follows, almost instantaneously, is a satisfying, muted growl from the exhaust and a whoosh of speed.

Both the CLK350 and CLK550 are equipped with the seven-speed automatic, and we like this transmission. Beyond the extra gears, its control program works better than that on the Mercedes automatics of previous years. This one doesn't slack off when you need it most, kicking down to a lower gear fast, sometimes three gears at once, if you slam the accelerator hard. Alternate shift buttons, which allow selection of a specific gear, are located on the back of the steering wheel hub, right where fingers wrap around the spokes. The touch-shift manual mode works nicely.

The AMG model also gets a seven-speed automatic, labeled the AMG Speedshift 7G-Tronic. Its internal parts are beefed up to reduce shift times in manual mode and handle the power generated by the CLK63 AMG V8 engine (465 pound-feet of torque). Previously powered by a 5.5-liter V8, the previous AMG CLK was merely fast. With the 6.3-liter engine and seven-speed automatic, it's blindingly quick. Throttle response is instantaneous, automatic downshifts nearly so, and the manual control electronics are better programmed to hold a gear near the engine's redline, allowing high-rev, low-gear driving enthusiast drivers enjoy.

The CLK63 AMG we tested had a fluttering sound in the idle that was a bit annoying by Mercedes standards, but when we recalled it was a 475-hp engine, practically a race motor, it seemed a little less so.

The CLK Cabriolet AMG was already one of the most drivable cars in Mercedes' inventory, and with the new engine it's more so. It's not equipped with the Active Body Control or variable air suspension used on Mercedes ultra-luxury models, just good suspension tuning, good steering feel and crisp turn-in. Some Mercedes-Benzes will dutifully go along for the ride when driven hard, behaving quite predictably as they go. The CLK63 likes to be pushed, and when the driver finishes a go through an empty canyon, the CLK is ready for more.

The brakes on the CLKs stop the car with authority, and deliver a nice, easy-to-modulate pedal feel that's distinctly lacking on some Mercedes models. The CLK63 AMG Cabriolet is equipped with multi-piston brake calipers and larger rotors that kick everything up a notch, virtually eliminating the possibility of brake fade anywhere this side of a race track. The AMG is also equipped with something called Racetimer, which can record acceleration, top speed or lap times and store them for retrieval at the driver's request.

With its smooth aerodynamics, generally quiet manners and excellent anti-skid electronics, the rear-drive CLK Coupe is suitable for all-season use, in our view. Snow tires would remove any reservation, even in regions with lots of snow.

If you love top-down motoring, there's no real reason to pass on the CLK Cabriolet. With the top up it's almost as snug and quiet as the coupe. With the side windows up and fold-up windblocker in place, you could motor top-down on sunny days when the temperature is in the 40s. Best of all, there is no serious degradation in that tight, solid feeling that characterizes the CLK Coupe. Extensive use of high-strength steel alloys and liberal structural re-enforcements maintain the torsional stiffness and help minimize vibration. Mercedes claims the stiffness of the cabriolet's body is equal to that of the coupe, and we find no reason to challenge that assertion. Of course, those structural re-enforcements add weight to the Cabriolet, so owners are likely to see a slight reduction in fuel economy compared to the coupe.