Originally Posted by micknugget
I say the S4 is more sportscar oriented because besides the bigger engine than the A4, it has a sports suspension, upgraded rear differential, upgraded dual clutch automatic, summer only tires, aggressive sports seating, upgraded brakes, etc. It is clearly not a typical Audi designed for all weather conditions. It is designed to be a sports car version of the A4 giving up luxury for performance. The 335 can be altered thru options but it isn't the same IMO.
I think of the S4 like a Sport Line 335i, and both the 328i and the A4 are available with similar options. The rear diff is an option on the S4 too and the 335i now offers upgraded brakes over the 328i. So aside from not being able to get a 3.0T A4 (in the US) without the sport seats and available rear diff, they really are fairly interchangeable.
I actually think that Audi has a big opportunity with the B9 chassis to surpass BMW on the sportiness and handling front in this class. The F30 was a small step forward from the E90 and leaves a large opening for Audi to get this next round right. Of course they'll probably make it bigger than the current B8, which will totally remove it from my consideration.