It looks like a 100% crop.
on the d800 with the 24-70 though, yes! must have grip for comfort and balance :P
I use the 24-70mm Mark II on the a7R, and being that this set up is half a kilo lighter than the 5D3+24-70mm Mark II I find it easier to handle in spite of the lack of a big grip.
The 24-70mm Mark II performs quite specularly on the a7R. It is a much better lens than Nikon's 24-70mm, and the Sony/Zeiss 24-70mm 2.8 for that matter as well. The Canon 24-70mm Mark II out resolves Canon bodies, on the a7R it provides the same sharpness that you get out of Sony's primes, like the 35mm and 55mm.