Well the S4 is probably a bit quicker than the 335 off the line however driving thrill would probably go to BMW. Audi has to figure out a way to put the engine behind the front axel. That means pushing their wheel base out further and moving the engine further back in the engine bay.

Oh yea, i dont think that any American magazine ever said that the M45 was the better drive and performance car...they just said for the price its worth it.

Just one of quite a few others:
http://www.germancarzone.com/showthread.php?t=283 (Motor Trend: BMW 545 vs Infiniti M45 Sport vs Mercedes E500 vs. Cadillac STS V8.)