ive had both a rs4 and an autech s1 not s2 but there was a huge difference in performance. the rs4 swayed like a boat and the 260 doesnt. autech is manual (big plus) although i miss the sunroofs in the rs4. the autech goes faster (stock). autech has pretty gauges in the centre console and 4 wheel steer. and the autech can do helicopters, tried in the rs4 and it scared the shit out of me whereas the autech smoked the tires and made me dizzy
an rs4 can be brought to the same spec but there is more difference than just adding power.there is brakes/suspension, dunno if s2 rs4s have 4 wheel steer, finding one in manual or making one, the body kit,
honestly out of the two i prefer the autech the only thing i miss is the sunroofs but the autech looks cooler, goes faster, handles better and mine is currently on 185,000kms