The Audi A6 is dynamically superb. Quattro models deliver a feeling of being on rails, benefits of a rigid chassis, a well-engineered sports suspension, and Audi's superb all-wheel drive.

The A6 ride feels firm but is nicely damped for sharp bumps. It's among the best in class in comfort and near the top of class in handling (bested only by BMW). The ride is notably firmer for 2008, thanks to the 18-inch wheels that come standard (instead of 16s or 17s). Those who prefer a more comfortable ride will want to opt for the no-charge 17-inch wheels. Those who prefer a firmer ride with more responsive handling can choose the sports suspension, 19-inch wheels, or both.

The adaptive air suspension optimizes road holding and comfort. It's a marvelous invention that really helps keep the car securely fastened to the ground.

The Servotronic steering allows precise control and the A6 goes exactly where the driver wants it. Grip is excellent. Drive the car to its limit and you'll encounter a small amount of understeer. The highly rigid chassis gives the car the feeling of being carved from one block of material. This rigidity allowed Audi engineers to precisely tune the suspension. The A6 uses Audi's proven four-link front suspension and the self-tracking trapezoidal-link rear suspension adapted from the A8.

The flat torque curve of both the V6 and V8 engines gives the A6 a feeling of smooth, sophisticated power and responsiveness at all speeds.

The 3.2 V6 delivers strong response from 2000 to 6000 rpm. It offers lots of torque, giving it quick acceleration off the line and responsive performance at all speeds. Audi says the 255-hp 3.2-liter V6 is capable of propelling the A6 from 0 to 60 mph in 6.8 seconds, which is reasonably quick. We were able to easily work through traffic between Milan and Lake Como in an A6 3.2 sedan and felt no need for the more powerful V8. This impression was reaffirmed in a subsequent drive of the A6 Avant 3.2 in Italy's Dolomite Mountains. Not only was the V6 in full compliance with our lead-footed driving habits, if we hadn't occasionally looked in the mirror, we couldn't have told whether we were driving the sedan or the wagon as we raced up and down the twisting alpine roads. The V6 gets an EPA-rated 18/27 mpg City/Highway with front-wheel drive and 17/25 mpg with quattro.

The 4.2 V8 features direct injection and produces 350 horsepower, enough to propel the A6 4.2 from 0 to 60 in 5.8 seconds, which is quite quick indeed. Better yet, the increased power comes without much of a penalty in fuel mileage. The 4.2 gets an EPA-estimated 16/23 mpg City/Highway, respectable for a sports sedan. The A6 mounts its engine longitudinally, rather than sideways, improving the flow of power between front and rear wheels and improving driving dynamics.

The six-speed automatic transmission is super smooth and adds considerably to the joy of driving the A6 with its responsive performance. If the mood strikes you, select the Tiptronic mode and shift manually via the gearshift or steering wheel paddles. We found it worked exceptionally well in Drive: It always seems to be in the right gear, whether quick acceleration is wanted or smooth cruising is preferred. The CVT in the front-drive model is surprisingly sporty and is the perfect choice for the owner whose driving terrain is mostly urban streets.

The S6's V10 is refined and forceful. It is perfectly happy cruising in traffic, but is more than willing to launch the car ahead of traffic if you find a gap. The S6 is capable of a 5.1-second 0-60 mph sprint and can cover the quarter mile in 13.4 seconds. While these are certainly impressive numbers, some V8s do as well without the V10's high level of technology. The V10 suffers a fuel mileage penalty, as it is EPA-rated at 14/19 mpg City/Highway. While the V10 performs admirably, we found either the V6 or the V8 to be plenty powerful and not nearly as expensive.

The S6's suspension settings are even firmer than those of the sports suspension available on the other models. We found the S6 to be firm, but acceptable on rough Chicago streets. It is considerably firmer than the BMW M5, however, and some drivers will simply find it too harsh. While the S6 is certainly a wonderful car, we think it is bested in both ride quality and handling by the M5.

One advantage the S6 does have over the rear-wheel-drive M5 is the Audi quattro all-wheel-drive system. The power split 40 percent to the front wheels and 60 percent to the rear, giving the S6 the handling advantages of a rear-drive car, but the slippery pavement traction of all-wheel drive.

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