But if you can, why not take the R50S? That's a 550i taken from 407 ponies and boosted up to 620 horsepower. Controlling that oomph will be a Racing Dynamics sport suspension, locking rear differential, and a brake system with slotted discs that can handle 800 degrees Celsius. Making it sound good will be a new exhaust, and making it look good will be a minimal bodykit featuring a pair of dual pipes and 21-inch forged wheels.
[Source: Bimmer Today (translated) via BMW Blog]