After seeing the 70D specs I have real doubts about buying a 6D. Yeah, what Im talking about??? FF sensor!!! Kill me now. But as far as overall performance the 70D just topped my choice of usefull specs vs. 6D, When I travel to NYC to buy my new body the balance is to the crop body for sure :S (If my budget/credit card flunks on the 5DmkIII)
Why not? APS-C isn't worse than the best 35mm cameras with the best film material we had in the 1990ies - and if you have a good lens arsenal why change everything?
I am really glad with my 600D for movies and the 5.6 400:
5.6 640 effectively
5.6 1920 with 3x zoom (one physical pixel = 1 1080p pixel)
With FF? never possible.
The 2.8 100 acts as a 2.8 160mm which his very helpful and the 10-22 ultrawide does a reasonable job. I really prefer to wait for a FF mirrorless (if that will happen) for high resolution/low DOF/reusing my FD lenses and a compact HQ camera and ... use APS-C longer than planned initially.
If ISO 1600 is very clean with the 70D there is no reason to change the sensor format FOR ME.