[bradleyland]

They each have their strong points. The M4 is so much louder, and it has all those wicked sounding over-run crackles and pops. I'm not sure a crappy cell phone video is the best tool for judging a sound battle, though. I've never heard an M3 GTS or M4 GTS in person, but I have heard a regular S65 and S55 with various exhausts, and the S65 sounds like pure sex. The S55 sounds very mean, but it ultimately comes down to preference. If you prefer the sound of a V8, the S65 is going to win every time. If you like the raspy rip of an I6TT, you'll prefer the S55.