Beware - if you use the articulating screen and the crop video functions, you will lose those. Crop to full frame is a big difference in terms of lens reach for telephoto as well as the wide end on something like the 24-105 (which i had previously on my t2i).
I went with the 6d, if nothing else because i wanted better wide end on the 24-105 and i wanted better high ISO jpg capability. I can only imagine the 5dmk3 being an even better camera with its autofocus and build quality, but i couldn't justify the extra $1k when 2 features i wanted (GPS and WIFI) weren't included.
I might be using video once in a while, but action and candids for the most part.
GPS and wifi are also just 'extras' for me. I really like the specs on the 5D's focus system (41 cross points vs 1), 61 focus points (vs. 6D's 11), 1/8000 vs 1/4000 max shutter speed, and 6FPS vs 4.5FPS. Still trying to justify a $3500 purchase though...