I have a 05 M6. I originally install a Magnaflow cat-back system. The sound was a little tame still so I replaced the mufflers with a set of magnflow resonators. It sounds great now!!
I don't feel a diff in power and I have not raced for time so I can'tay if I have lost anything but if I have it is not much. I am sure my new headers and cam will make up for that.
