At the risk of going off on a tangent, I still believe that the answer is the same for the same image. D800 or D4 doesn't matter to me if it's the same amount of the frame.
Now if I'm cropping tiny portions of the D800 and comparing the same number of PIXELS on the D4, then I need more shutter speed on the D800 because the angle covered is smaller and movement is exaggerated. So about half a stop sounds right which what seems suggested. But ONLY if I'm enlarging more with the D800 image than the D4. Same angle of view, same shutter speed.
Technique may vary a bit especially if you don't have a grip on the D800. I find the larger body is a bit steadier I think just from inertia. But I think it's a slight difference, and maybe psychological.
I find they are a good combination for lots of two body shooting. For example I use a 200/F2 on the D800 for basketball for far court, and a fast short lens on the D4 under the basket. Then I crop the D800 shot more heavily, giving me about a 300mm instead, this lets me shoot at F2, vs. something like F2.8 or worse F4 with a longer lens.