I moved from T1i to 60D. I am still shooting the 60D. Last December, I bought a 5D, the original one, just to play with full-frame. I am liking it. My 60D is getting less use these days. I intend to keep it because the 60D and 10-22 gives me the best UWA setup Canon makes. That and my 100-400L is (apparently) longer on the APS-c body.
On to your issue: 5D2 vs 6D? As stated, I like FF and am considering an upgraded body. Like you, the 5D3 is off the table. That is too much money for an amateur like me. When considering the differences between the 5D2 and 6D, I am left with this. The 6D is newer. Newer processor, newer sensor, newer focus system. The oft listed short-comings of the 6D, 1/180 sync-speed and 1/4000 max shutter are almost insignificant. I went through my photos for the last year or so. I have one at 1/5000 and one a 1/6400. Both of them were wide open on f/1.8 lenses. Stopping down would have improved those shots. HSS negates the less-than 1/6 stop difference is sync-speed. Both of these specs exist solely so Canon's marketing department can upsell the 5D3.
In every other respect, as far as IQ goes, the 6D is superior to the 5D2. At lower ISO, the difference is probably not visible. As ISO climbs, the 6D leaves the 5D2 behind. It actually gets reviews better than the 5D3 at higher ISO settings.
One thing I don't like about the 6D (and the 60D for that matter) is that the top-deck buttons only do one function. The two-functions-per-button of the 5D (and 5D2, 5D3) give me direct access to more settings.
I don't know if the 6D has MFA, but that does not matter to me. I've never needed it. It must be said here that I don't own any f/1.2 or f/1.4 lenses. I have several f/2.8, f/2 and f/1.8 primes, and one f/2.8 zoom, and have never needed MFA.
Add to all this the fact that right now the 5D2 costs $200 MORE than the 6D and I have a winner. If/when I upgrade my 5D, it will be to a 6D. Even if the 6D were $200 more than the 5D2, I think it is worth it. Thank you. Your question has helped ME think this through.