Upload & Sell: Off
#1. My three 5d2s, under the same low-light conditions as the 5d3, track pretty well, and better than the 5d3. When the 5d2s give up in AI-Servo, the 5d3 also won't have a chance of tracking either (just hunting without telling me it failed to focus), so I switch to one-shot mode (which turns on AF assist) and the 5d2s still lock pretty well on the moving subjects. If I try that with the 5d3 (switching to one-shot on moving subjects), it's pretty much guaranteed to miss 90% of the time.
In one-shot mode using AF assist, my 5d2s lock much faster than the 5d3 on ANY subject, moving or standing still. For an "upgrade," my disappointment in this kind of performance shouldn't need explaining.
#2. The 5d3 has the option of 3% focus point - which the CPS rep said will make focus tracking less reliable and the one-shot focus slower, etc. in low light, and so I am going to give the 8% coverage focus point a shot. I don't use expanded points for receptions because they just lock onto the wrong target too often.