The S4 weighs 200-300 lbs more than the M3. Even with the same amount of power, it would be hard to keep up. They have the new active rear differential for better cornering... but in the real world, it doesn't handle as good.
The S4 would be a good all around street car but definitely not a track beast. I'd pick an Evo any day over the Audi for track duty. You can easily tune an Evo for 400hp for about a thousand dollars and it'll be great fun. Handling on the Evo X is the best besides the GT-R for an AWD car.
For a 4 door sport sedan, this is what I think works:
Street - S4
Street/Track - M3
Track - Evo
Last edited by Z K; 10-01-2012 at 12:57 PM.