I bought my 6D earlier this year, conscious of the fact that the AF being underwhelming on paper. I've been loosely following this thread and similar ones online, seeing people say the 6D's AF is anything from "completely useless" to "actually, pretty good!". Most photos I take are of stationary things, so it's no big deal.
This weekend, I visited a place called Go Ape — an obstacle course through the trees in a British forest. I was taking photos with my 6D and 70-200 f/4 (no IS) and was kinda worried since the weather was typically dark and grey, we were under tree cover and I had to take photos people people sliding down zip lines at fairly high speed.
Thankfully, my fears were unfounded. The AF in the 6D performed amazingly well and I was getting some superb shots! Sure, the AF isn't as good as the 5D3's, but it's way better than a lot of posts and articles would lead you to believe.