I never (or seldom) use AF, so I know little about it. I am worried more, at this point, by manual focus.
I ’m caught between the devil and the deep-blue sea, with the X1D and the D810. For example, I do a test indoors in a room with not too much light. And I focus on a particular object and shoot (for each camera) at f/16, f/8, and f/3.2.
Well, with Live View on the D810 (Otus 85) I can hardly see (I can’t see!) to focus clearly in LiveView and I need the Z-finder even to do that. While, with the LiveView on the X1D (90mm), I can actually see to focus.
As for results, the D810/Otis is sharper and the X1D/90mm is less sharp, but still just sharp enough to be usable. The problem with focusing on the X1D, if I press the magnify button it goes up to a certain point, but no farther. There may be a way to go to a higher maginfication, but I have not found it (I probably have not yet found a lot of things on the X1D). And the focus-by-wire on the X1D is so touchy that even the slightest move is often too much, but I “CAN” do it. I can focus.
In the above case, the ability to focus and see in LiveView on the X1D makes it the camera for this particular “darker” environment, simply because the D810 can’t really see. Yes, I could get a flashlight to focus with and then turn it off, but there is a point where the work being done is not worth the work being done, etc.