Numbers are numbers, field is field and I would not buy a gear based on DxO reviews. Just remember the review of the 70-200/2.8II by them. It fares worse than the Sony 70-200/2.8 G...
We are talking here of pure academic assessment by guys in white coat in an immaculate lab. In absolute terms, for sure the D800 sensor will out-resolve the 5D3's. Period. No need whining. Now, just pixel-peep the Still-life 6400 at http://www.imaging-resource.com/IMCOMP/COMPS01.HTM
and compare between D800 and 5D3. Not surprisingly, D800 will out-resolve the 5D3 in the fabrics area. This is to be expected as fabrics are sort of micro 3D textures that require lots of resolving power for extracting details. Good if you are in the garment industry. Now, move around anywhere else in the pictures and conclude by yourself. For me, there's a two stops difference in ISO. As far as I am concerned, that's what I am looking for.
So, what's the big deal here ? ISO or resolution ? Just make you pick and be happy ever after.