No, sorry, I don't have such a comparison nor have I been able to find one.
I'm about to move (a long overdue move at that) from a D-80 to a 6D, I never ever expect to own another Nikon.
I've read 6D reviews, specs and pixel peeped until my own focus blurs, the 6D sounds just about perfect for me, I expect to start with just the 40 mm pancake.
So, here are my questions
About the focusing screens;
Standard is the Eg-A II, Standard Precision Matte.
Optional is the Eg-D, Precision Matte with Grid. I like a grid in the finder, although lack of a grid is in no way a deal killer.
Also Optional is the Eg-S, Super Precision Matte. SUPER PRECISION, I really like the sound of that!!
I'm anxious for input from 6D (and 5D II?) users that have used two or more of the three Canon screens, I suppose I shouldn't be close minded about aftermarket options.
At wider lens apertures, is the Super Precision Matte Eg-S significantly sharper showing focus than the merely Precision Eg-D?
At smaller lens apertures, say f-4, f-5.6 and smaller, do either the Eg-D or Eg-S darken objectionably to the point of uselessness?
Anything else I'm not thinking to ask?
A little insight to my camera operation style, I go back to the film days, the only things I miss about film are the loading, rewinding and release tricks to get multiple exposures. And I'm quite happy to miss them, right along with automotive carburetor and valve adjustments though I still far prefer driving a stick.
Autofocus to me is a gimicky luxury, I do not expect autofocus to take photos for me. At the first sign of autofocus wavering, manual I engage. I'd much rather manual focus than dink around with shifting autofocus points instead of activating the shutter. I have little (read, no) interest in even learning how to shift autofocus points, yeah, I'm that old.