Well, remember the other thread:
http://www.germancarzone.com/showthread.php?t=5650 (Automobile mag: Dyno of 335i coupe, and 0-60, 1/4)

That dyno test of the 335i seems to suggest it's putting out something more like 350hp and 350lb-ft (around 490Nm). Seems plausible to me and would go a way towards explaining why it's faster than the S4.