The M6 is very, very fast, but it could be faster, as it stands, it tops out at just shy of 200 mph, whereas the M5, tops out at the exact same speed. The advantages of the M6 over the M5 are numerous; the M6 has a carbon roof which lowers the center of gravity making it handle better than the M5, and the obvious fact that is in a coupe versus a super saloon.