RS4 and S4 use the same motor. Only the rest piping and turbos and etc are different. Which means, the Engine was tuned up by whichever tuner, and shows it's doable.
For S4 to come close to RS4's performance, what really takes is $.

I admit it is safer to start with RS4 if we talking about hp war here. And I also admit that Recaros, and all those nice neat features of RS4 is making me drool. But, I believe a tuned up S4 can be just as much fun (or at least close enough) as a stock RS4 with much less $ spent. And don't forget that utility of both RS4 and S4 are at the same level. :)

Don't ask what college can do for you, but think who you can do in college~! :-D