2007 Audi S6, 2007 BMW M5, and 2007 Mercedes-Benz E63 AMG

A big engine in a mid-size car--it's been proven to make our glands swell and our mouths water at least since Pontiac stuffed a 389-cubic-inch V-8 into the 1964 Tempest. Today, the German premium brands are its most fervent practitioners, putting tarmac-peeling power into almost-stock-appearing, mid-size sedans. This summer, two newcomers, the V-10-engined Audi S6 and the Mercedes-Benz E63 AMG, will attempt to dethrone the current four-door king of the fast lane, BMW's awesome M5.

To challenge the M5's V-10, the S6 packs a V-10 of its own, but the Audi is able to extract only 435 hp, compared with 500 hp for the BMW. The S6 acquits itself better in the torque department, besting the M5's 384 lb-ft by 14 lb-ft. Mercedes comes the most prepared, at least on paper, with a normally aspirated, 6.2-liter V-8 that delivers a massive 507 hp along with 465 lb-ft of torque.

On the road, these differences in power and torque are less obvious than expected. After all, it's not only the numeric potential that matters but also what you can do with it. According to their manufacturers, the E63 can storm from 0 to 60 mph in 4.3 seconds, and the S6 performs the act in a less explosive 5.1 seconds. Our test results for the M5 put it right in between at 4.7 seconds. Of course, in the wet, the all-wheel-drive Audi wins the stoplight grand prix without even trying. On the autobahn, all three cars will beat the train and challenge the plane. Although the E63's maximum velocity is governed at 155 mph, AMG will reset the limiter to 186 mph if the customer pays big bucks for the 0-3-0 option [see page 88 of the July 2006 issue for more information]. The downside of leadfooting these beasts is a drastically reduced range and dramatically higher fuel bills. The M5 suffers more than the rest, because drivers invariably operate it in manual mode, and because it takes all 500 hp and the quickest shift setting to deliver the goods.

Visual judgments are more subjective. If you lean toward understatement, you may feel a little uncomfortable in the E63, which is dressed to kill. Its front spoiler was obviously designed to suck in air rather than to divert it, the small rear air deflector produces plenty of much-needed downforce, and the tapered sills help smooth the airflow before it reaches the razor-sharp rear apron. The two-tone, polished aluminum wheels are shod with eighteen-inch Bridgestone Potenza RE050 tires, 245/40 in the front and 265/35 out back.

Were it not for the aggressive-looking, five-LED running lights, the Audi would qualify for Performers Anonymous. The subtle visual modifications include a different grille treatment, four chrome exhaust pipes, slightly wider front fenders, flared lower door panels, and restyled nineteen-inch wheels fitted with Continental ContiSportContact 2 rubber (265/35 all around).

Although its visual impact was somewhat lessened in Europe by a look-alike sport package that is available for any ordinary 5-series, the M5 still stands out as one of the least controversial BMWs designed under Chris Bangle. It's a chunky piece, with a wide, low stance that spells presence with a capital P. The nineteen-inch wheels wear Michelin Pilot Sport footwear, 255/40 up front and 285/35 at the rear.

Inside, the M5 is somewhat stark, albeit at a high level. In addition to the love-it-or-hate-it iDrive, the quickest sedan from the Bavarian Motor Works offers a bewildering selection of setups. First, you must decide whether to change gears manually or automatically. That's an easy choice: in auto, the seven-speed SMG gearbox is still either unacceptably jerky or unacceptably slow. Second, you have to choose between 400 and 500 hp. Why? God only knows, but we suspect the engine always starts in four-fifths mode to curb its fuel consumption. Decisions three and four concern the shift speed (six to choose from) and the damper setting (three to choose from). What's next? Switch off stability control, or start fretting with iDrive? In total, there are twenty different settings that allow almost countless permutations. No, we didn't try them all. But we grew to like the combination of P500 (500 hp), M Dynamic Mode (heightened stability-control thresholds), EDC in normal damping mode, and S4 (fourth-fastest shift speed). You'll want to store your preferred mix and access it via the M button on the steering wheel.