The BMW is much more high-strung than its AMG rival. Its hoarse but melodic engine needs to be whipped to 7900 rpm to produce its peak of 333 horsepower. If you insist, it will briefly rev to 8000 rpm, albeit with protesting valve-spring clatter. Although the drive-by-wire accelerator works with telepathic spontaneity, there's a zero-lag Sport button for even more prompt throttle response. The six-speed transmission is geared for ultimate progress, not for cruising, so it's possible to run out of revs in sixth on a fast downhill stretch of empty autobahn. Although the 3246-cc straight-six has to turn 4900 rpm before reaching its 262-pound-feet torque plateau, the Bavarian engine never feels short of breath. Quite the contrary: The BMW reels the horizon in at an astonishing pace whenever you put your hoof down, even if the shift lever is in fifth or sixth. The M3 will sprint from 0 to 62 mph in 5.2 seconds. Moreover, we observed a respectable 17 mpg, the best fuel economy in our trio.
Although it falls short of the BMW and the Mercedes in terms of displacement and power, the Audi is hardly a sluggard. Helped by a close-ratio transmission and Quattro four-wheel drive, the S4 Avant will hurtle from 0 to 62 mph in 6.0 seconds. The top speed is, of course, electronically limited to 155 mph for all three cars in Europe. The Audi's twin-turbo 2.7-liter V-6 spreads its maximum torque of 258 pound-feet from 1850 to 3600 rpm. Although the V-6 is capable of revving to a strained 7000 rpm, its understated, almost pessimistic 250 horsepower is delivered at just 5800 rpm. If you keep the turbochargers wound up, you'll be rewarded by truly amazing midrange acceleration--from 40 to 65 mph in fourth, the portly wagon is one full second faster than the muscular M3 coupe, and from 50 to 70 mph in sixth, the gap widens to an even more impressive 1.8 seconds. Thanks to this flexibility, you don't have to change gears all that frequently--which is an asset, because the shift action is rubbery, and the indifferent clutch is heavily spring-loaded. Fuel consumption? A middling 16 mpg.
At first, the Audi is less rewarding to drive than either the C32 or the M3, which are more chuckable and decidedly tail-happy. But it doesn't take long to adjust to the S4's engine and handling and to start enjoying the grip, the tractability, and the bottom-end grunt. The Avant doesn't respond well to late, violent inputs--even with the skid control deactivated, such behavior provokes excessive understeer and lots of wasteful mid-corner wheelspin. The S4 is at its best in the hands of a calm, committed driver who chooses his line carefully, turns in smoothly, and is back on the throttle as soon as the nose starts changing direction. Going ten-tenths in the Audi entails very little drama, but the Avant can carry enough momentum out of a bend onto the following straight to give its rivals a run for their money.