The D810 is great and a really solid improvement over the D800. If I were Kevin, who has all my old equipment
, I'd sell the D800 and keep the D700 and the D810.
There is still something special about the D700. Just a no-nonsense solid camera with lovely color rendering. I should have kept it, but it would have put a dent in my serial acquisition plans.
I'm interested in the D850 especially for the articulated screen (which I have on my D500)--and all the other D500-like advances. I do some "studio" work for the magazine that has me standing on my head to compose with the fixed screen.
One thing I will miss about the D810 is the ability to use it as a master controller for multiple flash units. D850 has no built-in flash, but consequently better weather sealing.
Obviously, I've been reading too much about these cameras.