Upload & Sell: On
The 5d2 and 6D use the old style AF points and their outer points are pretty much useless in anything but very good daylight. The 5D3 has an AF system much like your 7D only much better.
Seems the 6D has the -3ev cross-type center point with 3 crosses, the 5D3's center point is -2ev with 4 crosses and has other points that have the same cross-type functionality sans the -2ev.
You get the 5D3 for it's AF, soon to be; AF at f8 and full HDMI out for video, 2 card slots, 100% viewfinder, stereo headphone jack, better build, etc...
A slight edge in IQ goes to the 6D but it's not by much; a quote from FM, it's lighter weight, has wifi n gps built in...
If you like, fully use the 7D's AF system, the 5D3 is your better body just because of the AF, from what I've read it's near as powerful as the 1DX.
Any of your listed bodies would be fantastic...