Upgrade D3 to D4 or D4s?
I went from the d3s to the d4 and the d4 had a little better pixel count, auto focus was about the same, noise level a touch more than on the d3s.
I sold my d4 because for shooting birds I need to be able to crop more so I bought a used d800e and it works better for my wildlife purposes (birds mainly). I use the battery grip on the d800e to get better frame speed using a d4 battery. I am quite pleased with the d800e.