I had 02 NOGARO S4 then sold it and bought A4 and now i am regret it that i sold it, and now im in the market for another S4. S4 is awesome by just chipped it will give you over 300hp that will make you smiles, and yes like other people say that you can mod your A4 as fast as S4 but if smog is your issue then go with S4. And another thing that no matter what you do to it then the A4 never gonna be the same as S4 like the M of BMW.