The American journalists from Motor Trend chose to take a "Head2head" duel between the Audi S8 and the BMW Alpina B7. 
The flag-ship from Ingolstadt is equipped with its new 4.0 liter TFSI V8 engine which produces 513 hp (520ps) and 479 lb-ft (648 Nm) of torque. The astonishing power is send to all four wheels thanks to Audi’s Quattro system via an eight speed automatic transmission. 
The BMW Alpina B7 is powered by a 4.4 liter V8 twin-turbocharged engine with 540 hp and 538 lb-ft (729 Nm). The power is sent via an eight speed automatic transmission to the rear wheels and optionally, to all four wheels
If you want to see who won this duel, check the video below.

Source: Motor Trend