Don't know what else could answer Ray's question other than for him to do the visual test himself with both camera models.
I won't be testing the D850 any time soon. My D810 is not saleable because it fell out of a shopping trolley about a year ago. It crashed onto a concrete floor from a height of about 1 metre. The 14-24/F2.8 Nikon zoom was attached, so it was an expensive package.
I immediately drove to the nearest police station to report the accident for insurance purposes. Unfortunately, when I returned to my home base I discovered that I wasn't insured. I've been in the habit of accepting travel insurance as a free bonus by paying for my airfare with my Gold Class Master Card. I wasn't aware that such insurance applied only to overseas travel. Silly me!
On this occasion I was traveling in Australia on domestic flights, with my female partner. Whilst she was doing the shopping, in Darwin, I was wandering around the shopping centre photographing Aboriginals. When she came out of the supermarket with a trolley loaded with food items, I offered to push the trolley, because I'm so magnanimous and compassionate. However, the camera slung around my neck tended to bang against the top of the trolley, so I placed it in a compartment at the top of the trolley, which is probably the place where ladies place their handbags.
Unfortunately, I didn't realize that the rear of that compartment was open. As I pushed the trolley over rough ground in the car park, the camera fell out due to excessive vibrations. When I picked it up I could see that the lower left corner of the camera had split open. The zoom lens appeared to be okay, except for a slight resistance close to the 14mm end, as I turned the focal length ring. For some reason the auto-focus didn't work but the camera was still usable with manual focusing. I was looking forward to buying Nikon's next full-frame offering. This accident occurred before the D850 announcement.
However, some time later, back at home base, I began fiddling around with the menu settings again, trying to get auto-focus to work. This time I succeeded, surprisingly. Perhaps the problem was similar to the problem I've occasionally experienced with my home internet service. For some inexplicable reason, on a few occasions, I've been unable get an internet service, even though everything appears to be working. The solution has been to switch the modem off, wait a while, then switch it back on.
Now that my D810 is fully functioning, I decided to plug up the open crack in the corner of the base, where it hit the ground, with glue, just to make sure no water or dust gets into the camera body. I wouldn't be able to sell such a camera.
The bottom line is, I'm rather amazed at how robust this Nikon D810 is. I'll probably replace it with a D850 in a year or so when prices have dropped and the bugs have been fixed. In the meantime, I don't think it's likely that I'll go to the trouble and expense of hiring a D850 for the current price of $76.85 / Week for a minimum 6 months rental, just in order to compare image quality with my D810, because there are lots of other reasons to buy a D850, and I'll get the opportunity to do my thorough testing and comparison of image quality eventually.