Autocar tested the two round a track also. The M3 was 2 seconds faster in the dry if I remember correctly, and 5 seconds on a wet track believe it or not. I didn't until I saw the explanation - the heavy V8 in the front of the S4 means that in the wet, the nose washes wide far in advance of the M3, meaning that despite the S4's traction advantage, the M3 can nail it round wet bends.
Until they sort out the understeer and lifeless steering, the S4 will always be inferior to the M3 as a driver's car imo. Plus, it's got half a McLaren F1 engine
