Get a bunch of car enthusiasts to talk about German performance sedans and they'll typically start spewing four-letter...well, just four letters: AMG and M. The former refers to Mercedes-Benz's in-house tuning division and the latter to BMW's. Yet there's one more letter that is often overlooked: S. Audi's high-performance "S" line has been around for more than a few years, and the S8 -- the souped-up version of the standard-wheelbase A8 -- is particularly alluring, owing to its Lamborghini-derived V10 engine and roomy, handsome cabin.

Mostly unchanged for 2009, the Audi S8 sends a healthy 450 horsepower to all four wheels via a six-speed automatic transmission and Audi's Quattro all-wheel-drive system. The V10's peak output isn't as high as in the Lambo Gallardo, as it has been tuned for a broader power band that's better suited to a luxury car. But it isn't by any means lacking, either -- the S8 can sprint from zero to 60 mph in the mid-5-second range and will effortlessly run at autobahn speeds all day long. A sport-tuned adjustable air suspension, 20-inch alloy wheels, upgraded brakes and unique styling tweaks are also part of the deal.

But potential buyers should consider the alternatives before deciding on the S8. Hard-core driving enthusiasts might want to go for the BMW Alpina B7, which boasts blistering performance and sports-car handling. For raw power, there's the Mercedes-Benz S63 AMG, which packs a punch with more than 500 hp. Another choice to consider would be the alluring Maserati Quattroporte S with its Ferrari-sourced V8.

As such, the 2009 Audi S8 isn't the most obvious choice here. But perhaps one of the most convincing arguments for the S8 is its sticker price, as it comes in under $100,000 -- less than two-thirds the price of the Mercedes-Benz. "S" might not be the first thing one thinks of in the case of performance luxury sedans, but the oft-overlooked S8 offers plenty of performance value for the money.

The 2009 Audi S8 is a high-performance version of Audi's A8 luxury sedan. The S8 comes in a single well-equipped trim level. Standard features include unique front and rear fascias, 20-inch alloy wheels, a sunroof, bi-xenon adaptive HID headlights, auto-dimming mirrors, full power accessories, dual-zone automatic climate control, heated power front seats with memory settings, a power tilt-and-telescoping steering wheel, a parking assist system with a rearview camera, keyless ignition and entry, a power trunk opener, rear-compartment sunshades, Audi's Multi Media Interface, a navigation system, Bluetooth and a 12-speaker Bose audio system with satellite radio, six-CD changer and iPod connectivity.

Options include a solar-powered venting sunroof, additional leather trim, carbon-fiber interior inlays, four-zone automatic climate control and a premium Bang & Olufsen audio system. The technology package bundles adaptive cruise control, a lane-departure warning system and a blind-spot detection system. The cold weather package includes a heated steering wheel, heated rear seats and a rear-seat pass-through.

The Audi S8's 5.2-liter V10 makes 450 hp and 398 pound-feet of torque. Power is sent to all four wheels through a six-speed automatic transmission that allows manual gearchanges via paddles behind the steering wheel. We've clocked the 0-60-mph sprint in 5.6 seconds. EPA fuel economy estimates are 13 mpg city/19 mpg highway and 15 mpg combined.

Antilock disc brakes with brake assist, stability control and a full complement of airbags (side curtain, front-seat side, rear-seat side and dual front knee) are standard. Lane-departure and blind-spot warning systems are optional.

Crack the whip and the V10 engine pulls hard from idle to redline without letting up. The power delivery is so linear that the performance is deceiving. The automatic provides smooth and quick changes, although it can hesitate a bit when prodded for a downshift. Take matters into your own hands via the steering-wheel-mounted shift paddles and the transmission responds quickly to your commands.

The 2009 Audi S8 rides slightly lower on a sportier variation of the A8's adaptive air suspension. It still offers four suspension profiles to choose from -- Automatic, Comfort, Dynamic and Lift -- but each level rides a bit firmer compared to the standard A8 setup. In any mode, the handling is confident with minimal body roll, and the ride quality is impressive, especially for a car wearing 20-inch alloy wheels.

One quibble we have concerns the brake pedal. Although the brakes themselves are more than capable (the 4,600-pound sedan can stop from 60 mph in 112 feet), the soft pedal feel is a disappointment considering the S8's overall capabilities.

As with all Audis, the interior of the 2009 S8 is beautifully designed and furnished. Alcantara covers the ceiling and the rear package shelf, and along with leather, aluminum and wood accents lends a sumptuous feel to the cabin. Double-paned side windows contribute to the hushed ride while devouring interstates, and the 16-way-adjustable sport seats provide long-trip comfort and twisty road support in equal measure. Audi's MMI control for the climate and audio systems is fairly intuitive as modern interface systems go.