I have just bought a good used example myself. Having regretted selling my D500 and D800 combo to fund a Z6 kit, I found the viewfinder lag and blackout of the Z6 prevented good panning for motorsport, coupled with the lackluster AF. When I was able to frame a car this resulted in many unsharp images. And Yes I tried every variation of the different AF settings. I did get very good shots when it focussed, but my hit rate was very low compared to the D800 and D500. I bought the D850 probably on the same day you did, this Sunday I will give it a run out at the Harewood hill climb, since it has the same settings as a D500 I expect it to perform superbly. I have been using a D3 whilst waiting for the Z8 to come out and buyers to trade in there old D850's.