Thought I'd bring the 6D along with my 7D for an assignment today. It actually performs pretty well for sports, although it's' only really good for a 2nd body to go along with the 7D or 1D series. This was shot at ISO2000. Tracking with AI Servo wasn't too bad, but it felt like it didn't perform quite as well as the 7D. For good static, isolated shots, it's GREAT...especially in basketball arenas where the light is really bad.
Real life ISO performance blows away the 5D2.
I also think that the 6D calculates white balance a lot better than the 7D.