I went from Stage 2 S3 to RS4. Not much in it performance wise, but thatS it. Everything else is so much better about the RS, steering, brakes, linear power and the noise - I did have a Milltek though!! I say go for it, just make sure it has a warranty, and the brakes are new, best part of 1600 all in!! Every trip is just an experience. Well it wants to be, mine averaged 16mpg or so over 7000 miles!
Do it, you won't regret it.