I`d like to see some D850 discussion here. Probably it is too early?
Hi Vincent, This started out as a D850 wildlife discussion but got a little side-tracked with the debate around the D750.
Thinking about your post, I arrive at a slightly different list I care about for my wildlife shooting. Quite a bit of it requires long hikes in remote areas or across rain forests, which may explain this. In order of priority, I'd say my requirements are these:
1. Reach - do I have sufficient focal length?
2. AF speed and accuracy - fast enough to always get the shot?
3. Hi ISO performance - is the shot of that owl sitting in the dark going to be good?
4. Schleppability - can I carry my gear over many miles without breaking my back?
5. Resolution - can I crop tightly and still keep a large enough image?
6. Shooting speed - can I get the right shot with a moving target?
As you'll note, color accuracy is not high on my list because I feel I can always fix that in post-editing.
Because of these priorities, a D500 is high on my list. DX has an intrinsic advantage with priority #1 and allows me to use a shorter (read: lighter) lens, where Nikon's 300mm f/4 PF is just right for me because it is sharp and super-light. In my view, priority #2 is only met by Nikon's 153-point AF - the older 51-point system isn't nearly as good, though not bad.
That leaves only the D5, which I consider too heavy, and the D850 as alternatives. D750 and Df are off my list because they have no DX and the slower AF, thus falling short of my two top priorities. I know some wildlifers place higher priority on shooting speed than I do, but that would not change the ranking between these bodies anyway.
The D850, with nearly as much resolution in DX format as the D500, is a seriously attractive alternative if its hi-ISO performance turns out to be as good as initial test shots suggest. I often carry two bodies and am definitely eyeing the D850 as my second one. But when shooting DX, I'm not sure which advantages it would offer me over the D500 for wildlife.