I've been following along with this. I guess it is about time for my two-cents worth. I bought a 5Dc about two years ago. Late last year I upgraded that body to a 6D. I've also been using a 60D for about four years.
Comparing the AF on the 5Dc and 6D is almost an exercise in idiocy. The 5Dc struggled in mediocre light, with fast glass, even using the center point. The outer points would regularly hunt in shady areas of broad daylight. My 6D has none of these problems. The outer points of the 6D will focus, accurately if not quickly, in light the 5Dc's center point would choke on. I have no complaints about my 6D's ability to focus, quickly and adequately, in good light. Likewise, it will focus accurately in very poor light, albeit a bit slowly at times.
When it comes to shooting things that move, I think the 60D is superior, in every way, to the 6D. Be advised that this may be inexperience talking. I tried some sports with my 6D and the 100 f/2, and Sigma 70-200 OS. Neither performed to the level they do on the 60D. If shooting moving targets, I use my 60D.
The 6D is my first body with MFA. As far as I am concerned, it doesn't need it. Or maybe I don't need it. None of the following list of lenses needed any MFA adjustment:
Sigma 70-200 OS
Canon 35 2 IS
Canon 100 2
Maybe MFA is more useful to those of you shooting f/1.2 or f/1.4 lenses. So far, I am happy with my 6D and its 'hobbled' AF system. Although, I must admit, I'd rather have a 5D3. Finances don't permit that.