Go to some get togethers and hear the options in person. Most owners are happy to demo their pipes and its fun to socialize with other M owners. Try and get the owner to take you for a spin when you hear something that sounds good. Free revs in a parking lot don't cut it and tell you nothing about drone. Again you will find most owners are happy to give you a spin or at least I have found this to be the case. Getting an exhaust you end up hating two weeks after you install it is no fun and completely unnecessary. Take the time to check out the likely suspects. You wont be sorry you got the right exhaust the first time.
2012 E92 Space Grey with fox red/black/black, comp, premium, DCT, premium sound, sirius, heated seats.