I tested both cameras.. 6D and 5Dmk2, and the 6D is way better than 5Dmk2..
I would say the center point from the 6D is supercharged.. WOW!.. Can't even compare with 5Dmk2
The new tech behind 6D with low light autofocus (-3EV) is a big improvement over any camera ever made.. IMO
You can really focus spot on in any light conditions.. impressive!!! And the images still sharp (using 85mm 1.2)
Btw, I really don't care if the camera has only 11 focus points.. I use the center point all the time (99.9%)..
My final words are.. the center point from the Canon 6D might be better for accuracy from any Canon camera ever build.. believe me, this thing is very powerful..
And the ISO performance BLOWS 5dmk2 and better then 5Dmk3