This is a tough comparison do to price. Remember guys the 4s is about a 90,000 dollar car. An M3 equipped with the s54 engine will be right there in performance. Again proof of how good the M3 really is. I think it would be all about the driver. Hey we even have a back seat and an engine that does not sound like a can full of rocks on cold start up. The 4s is an awsome car but how would the M3 perform if you put 30K more in it? It would not even be close. The M3 is truley a remarkable car.
2003 S4 Vehicle layout
Rear engine, awd, 2-door, 2-pass
Engine 3.6L F-6, DOHC, 4 valves/cyl
Hp @ rpm 315 @ 6800
Torque @ rpm 273 @ 4250
Transmission 6-speed manual
0-60 mph, sec 4.6