Well it is now confirmed that the 6D has 11 point AF with only one cross type point.
So you'll be using the old focus and recompose technique, no matter which camera you pick.
If I were you, I'd abandon ship and go for the D600. Looks like a much much better camera.
I i didn't had so many Canon glass i had dropped the ship few months ago when 5D3 was announced and go for D800.
I tried the D800. I even bought some high end Nikon glass to try with it. The D800 is a very good body, but finding Nikon glass is difficult. I mainly used the 24-70mm f/2.8G. It had such bad CA that it could not be corrected. Then, there is no equivalent for the 135mm L, the 24-105mm L, the 100-400mm L, none of my favorite lenses have anything nearly as good, and the price of the inferior glass is higher.
This takes away most of any high resolution advantage the body gives.
High ISO noise is also a issue, but if you stay at 400 or less, the DR is fabulous.
You might be unhappy trying to match your Canon lenses. After all, Glass is much more important in the long run. Nikon lenses have even more AFMA issues, they are glued together, forget any maintenance that you can do yourself, and live view on the D800 is slow and barely usable. Tethering software is not included, and when it is, its painfully slow. There are lots of little things that reading the hype does not tell you.