Scale can be a real bugger sometimes. The Eiffel Tower sure seems tall until you realize that a glorified TV antenna in Canada called the CN Tower is nearly twice as tall. Or, your husband may seem hunky until Ocean's 11 comes on and the hubby is reduced to a level somewhere south of a clock-tower-dwelling hunchback. With its exotic V10 engine and various other sport-tuned components, the 2008 Audi S6 performance sedan is a fine machine that offers its driver a mix of high-speed fun and comfortable on-road demeanor. Yet when compared to its prime competitors, the BMW M5 and Mercedes-Benz E63 AMG, the S6 starts to suffer significantly from scale.

Putting aside its lofty competition for a moment, the 2008 S6 has a lot going for it -- specifically, the 435-horsepower, 5.2-liter V10 engine that's based on the V10 found in the Audi-owned Lamborghini Gallardo exotic sports car. Despite having less power, the S6 version features a fuller power band that's more befitting a luxury sport sedan. Further enhancements over a regular A6 include significant suspension tuning, larger wheels and brakes, unique styling elements and aggressively bolstered front seats.

The rest of the S6 is typical Audi. The only transmission is a six-speed Tiptronic automatic transmission with steering-wheel-mounted shift paddles, while its ubiquitous Quattro all-wheel-drive system should appeal to those who want maximum performance and maximum bad-weather traction. Inside, the cabin is constructed with the same impeccable panache and quality that sets the regular A6 apart in its class. All together, the 2008 S6 is a package that offers a lot of goods for a price that's at least $11,000 less than its two German rivals.

However, the question therefore arises, how important is value for shoppers of high-performance sedans? If one can afford an S6, are the extra thousands needed to buy an M5 or E63 AMG that prohibitive? We'll leave those answers to your checkbook, but price aside, the S6 simply does not measure up with the BMW or Benz. Both out-accelerate the S6 by a second or more in the 0-60-mph sprint and the quarter-mile. Both are far more at home on twisty roads than the Audi, which is pudgier and more nose-heavy, lacking the light-on-its-feet feel of the other two. Plus, its stiff ride makes it less comfortable than its hard-core competitors. It's far from a clock-tower-dwelling hunchback, but to the 2008 Audi S6, scale is still a real bugger.

The 2008 Audi S6 is a high-performance version of Audi's A6 midsize luxury sedan that comes in one loaded trim level. Standard equipment includes 19-inch wheels with performance tires, a sport-tuned suspension, upgraded brakes, adaptive bi-xenon headlights, a sunroof, a power tilt/telescoping steering wheel, dual-zone automatic climate control, heated front sport seats with driver-side memory, leather upholstery, Bluetooth, Audi's Multi Media Interface (MMI) system and a Bose surround-sound system with satellite radio and a six-CD changer in the glovebox.

Optional equipment includes the Technology Package that contains a navigation system, voice recognition, keyless ignition and rearview camera with parking sensors. The Warm Weather Package includes power rear and manual side window sun shades, and a solar sunroof that uses solar energy to power a ventilation system that cools the interior. Stand-alone extras include adaptive cruise control, heated rear seats, iPod integration and a no-cost option for less aggressively bolstered front seats.

The 2008 Audi S6 is powered by a 5.2-liter V10 that produces 435 hp and 398 pound-feet of torque. It sends that power to all four wheels via a six-speed automatic transmission that includes Tiptronic automanual shift paddles behind the steering wheel. In performance testing, we clocked the S6 going from zero to 60 mph in 5.7 seconds, with a quarter-mile run of 14 seconds. Fuel economy is 14 mpg city and 19 mpg highway.

Standard safety equipment on the 2008 Audi S6 includes antilock disc brakes, stability control, all-wheel drive, front-seat side airbags and full-length side curtain airbags. Optional safety equipment includes rear-seat side airbags, a rearview camera and Audi's Lane Assist lane departure system. In crash testing performed by the Insurance Institute for Highway Safety, the Audi A6 (on which the S6 is based) scored the highest possible rating of "Good" in both frontal-offset and side-impact tests.

Weighing nearly 4,500 pounds, the 2008 Audi S6 is no lightweight, and this is most noticeable when attacking a twisty road. Although steering is crisp, body roll is well controlled and handling is confidence-inspiring, the S6 just doesn't have the nimble feel of its lighter rivals. Around town, the sport suspension calibration gives a stiff-legged ride, quite out of character for an Audi and again not equal to the more forgiving yet still very capable setups of the M5 and E63 AMG.

Trimmed in leather, aluminum and birch wood accents, the S6's cabin upholds Audi's reputation as a builder of some of the finest automobile interiors. The S6's front sport seats are heavily bolstered to provide support during aggressive driving on a twisty road. The MMI control interface allows the driver and front passenger to operate entertainment, climate, communications and navigation functions. There's a steep learning curve involved, but the system is notably more intuitive than BMW's reviled iDrive. A split/folding rear seat with a pass-through provides additional cargo capacity should the trunk's 15.9 cubic feet not be enough.