I wonder, if your 5d2 was accidentally destroyed, you had enough investment in canon/zeiss lenses to stay with canon but didn't want to invest further in canon beyond simply being able to keep using your existing lenses, would you go for a 5d2 or a 6D, assuming web price of 6D comes down to parity?
Seems all you lose with 6D is no 1/8000 and one "C" setting. You gain more latitude in bracketing and the built in wireless. Plus/minus 5 stops bracketing is probably the most useful thing for me. Video (with this camera) is irrelevant.
Equally, the difference between 20.3 and 21.1 MP is insignificant, but could there be an improvement in shadow noise?