IMO, the stock body on an M6 looks perfect - Classy & Understated.
If you want more of a crazy widebody/stanced car, then something like a C63 AMG black edition might do the job. Things like front lips, vented hoods and diffusers are still great add ons to the M6 without going over the top though.
A couple of body treatments look nice. But when you do every single one to a vehicle it can look cheap. Too many scoops and plastic wideners just remind of the 80's American cars and how they would add a bunch of plastic to a Mustang or Z28 to make it look faster. Only thing that car is missing is some rear window louvers.
It is hard to beat the beauty of the stock form...