This is symantics, because the 6D is the closest thing to the 5D2 and the comparisons are valid, but I want to point out that the 6D is more of a full-frame rendition of the 60D and less of a 5D2 replacement.
The 6D has more gadgets and and a shrank footprint, at the expense of ergonomics (button layout) and ruggedness, meaning they're choosing marketing over robustness, like they would normally for a Rebel or xxD line.
The difference in size alone should be a clear indicator, along with the slower, laggier shutter (which is just pure crippling??) and the required plastic top for the wifi/gps.
None of this doesn't mean it's a great camera, I'm sure it is, but it wasn't designed as a professional's tool, the 5D2 is. I went with the 5D2 and am still happy with that choice.
Plus, I'm 6'0" with big hands, so that made it an easy choice