Both the RS 4 and the S5 are fabulous cars. You would probably be happy keeping either for five years or more. The RS 4 may have some older technology than the S5, but it is light years ahead of everything else. If you want an RS 4, this is an excellent time to buy one. Audi has done what it always does ... built one too many instead of one too few ... and the last ones in inventory are being given away.