Funny. I made the exact same post a month ago, only I asked about 6D, 7D2, 5D3 too.
I just got my 6D a few days before Christmas.
I would have to say go for the 6D. Having a FF camera is very useful. Very, very interesting compared to just a newer crop.
I avoided shooting ISO 400 on my T3i, and I would never shoot above 800 ISO. I have seen people showing off select images from 7D that they have modified significantly in post that look good shot at 1600 or 3200, or even a few from 6400, BUT, a.) not all of one's images would lend themselves to such treatment, and 2.) who wants to do that degree of intensive PP NR on every image?
I have been shooting the 6D at 3200 and it looks fantastic. It looks great at 5000, and even good at 6400 untouched in PP. With some PP, I could make it look better, but I have not even been messing with it that much. (LR3 needed upgrading to LR 4 for the new camera). I got LR4 yesterday, and it really is better than LR3, contrary to my initial thinking. That ISo ability is huge, it means so many indoor shooting situations where I can avoid flash altogether, or use it only for fill. I LOVE it.
The inherently shallower DOF is great too. Not so much because I want to use primes wide open for heavy effects, but because it makes F/4 look like f/2.5 did on a crop body.
I may someday pick up the 7D2 (whenever that might appear), but I can wait a year after its release after the prices go down. My T3i still works great when I want "reach" from a crop body.
As for the 6D's AF, it may not be the 61-point system, but it also lacks some of the complications that go along with all that complexity. I don't generally shoot super-fast things, or at least not in super-serious situations where one certain try would not be just as good as the next try.
What I do love is the one big, bright center AF point in the 6D, which catches AF instantly in low light (-3 EV, whatever that means to you
). Supposedly the 5D3 may struggle with lags on dim light focus. The 6D also has big obvious RED AF points you can see in the dark too.
In any event, bodies are constantly depreciating, and new ones that are 2x better are always beig released every few years. Lenses hold their value. I can sit out a generation on bodies. By saving $1,000 on 6D vs. 5D3, I was able to buy an extra prime lens, and still pocket some cash.