I have been using a 650d to photo my boys playing ice hockey over the last year with reasonable results. Due to the low light conditions I am wanting to go full frame. I was looking at the 6d as its the cheapest but a friend told me its no good for sports photography due to poor autofocus, apparently I need the 5d mk3! Obviusly this is a lot more money and to be honest i cant really justify the cost. Basically I am looking for opinions on the 6d AF abilities for fast sports in low light. Any ideas? I currently have a Sigma 70-200 f2.8 lens.