Thanks again Eric, I appreciate your posts because I always find that they are carefully considered and I learn something. The extra sharpness in the edges and corners are important to landscape, astro and macro photographers, I think, and I'm working on developing more skills for these, even if astro is aspirational at this point. I love that edge to edge sharpness you describe.One place where Z mount is significantly better is with medium and wider lenses. Virtually every lens at 50mm and wider is sharper in the midframe to corners than the F-mount predecessor. That applies to photos which require midframe to corner detail - off-center portraits, landscapes, astro, environmental close ups, and even events with medium to larger groups of people. That's where the new wider mount really pays off. My initial Z lens was the 24-70 f/4. The center of the frame was about the same as the F-mount 24-70 f/2.8 lenses, but midframe to corners was noticeably sharper with the Z lens. As a result, I largely stopped using the F-mount lens and D850 for those images and moved much more quickly into Z gear.
There are lots of situations where you don't need midframe to corner sharpness - such as portraits, wildlife in flight, and general wildlife. There are also artistic images where sharpness is not a critical factor. With an F-mount camera that was okay because you had limited ability to focus as you moved to midframe and frame edges. But with Z cameras you can focus to the frame edge, so lenses that are sharp to midframe and frame edges is more important. Of course, because Z cameras can focus at frame edges, even F-mount lenses can be sharper on Z cameras than they were on F-mount cameras.
I know that I eventually will switch. In the meantime I may pick up a used d850 or d810 for landscape primarily. I expect the main driver to get into the z8 or z9 will be wildlife. But you have raised some considerations I hadn't thought of. I expect however that my skills wouldn't notice the difference for a while. Cheaper f used mount gear might get me in the game sooner.
I wish the z8 or z9 were available before I retired when I had maybe double my income....!
The important thing is to get out there and enjoy shooting. I spent all day in light rain yesterday and got some okay shots, still learning! Biggest issue was a fogged up viewfinder so I had to shoot with live view on my d500, with mixed results.