After trying the Z7 for a few weeks with a manual in my hand, I now feel I cannot go back to the DSLR world. Some people feel they will never go to mirrorless - probably because of the viewfinder (which is the major and probably the only difference from DSLR), and I was one of them. I did not want to give up the clear, real image of the glass prism: The EVF is like looking into a tiny TV. Having viewed the Nikon EVF, I changed my mind. The EVF technology is constantly improving. Even in Sony, the latest models like A9, A7III are better than old models. But the ultimate fact surrounding the mirrorless vs DSLR issue is that we cannot reverse or stop the flow of technology. The DSLRs are things in the past. (No worries for DSLR users; Nikon will support them for the next 10 years.) There are huge advantages of mirrorless compared with DSLR. Not least of which, ironically, is what you can see in the EVF. The EVF image quality simply has to improve more, including the refresh rate. Soon, all the mirrorless cameras will have an electronics shutter only: The current focal-plane shutter that comes with a mirrorless as an "add-on" is a thing in the past, just like the DSLR's mirror box is. For this to happen, the CMOS sensor read speed just has to be increased... The camera technology is heading in the right direction...Heartily agree with that. Unfortunately no matter how much tweaking Nikon does with the firmware (yet to be seen) the Z7/Z6 will never be able to match the AF capability of the D5/D850D/D500...that's at least a generation away yet. That being said the Z7 is a sweet little camera and joy to use...sad to say my clunky D850 is going to collect a lot of dust over the winter sitting on the shelf waiting for the birds to return next season. What is clear to me is that mirrorless is next evolution in photography. It's surprising that Canikon took so long to recognize that and start responding. I predict that at most we're going to see one more pro-DSLR release from Canikon, and after that the DSLR market will fall off a cliff. Really.
Now, my impression on the Z7 + 24-70mm: It is a very solidly-built pro camera. Its viewfinder is superb. The AF is very good, even with the FTZ adapter with AF-S Nikkors, under AF-S (single AF) mode. I was a bit disappointed with the AF-C (continuous) performance. The Z7 is a $3000+ camera after all. It should perform at least as good as the D850. (Not fair to compare with $6500 D5.) Having said that, the Z7 distills all the features of the D850 in a much more compact, lighter body, and yet its hand-holding grip is as solid as any pro cameras. And it is a mirrorless with all the benefit mirrorless can offer. Also, the Z7's in-camera VR is simply amazing, a hand-held 1/2 sec shooting at 24mm is possible. I was also very much impressed by this "S-line" 24-70mm f/4 lens. It performs great even at f/4 wide-open. Nano-crystal coating prevents ghost/flare very effectively at night. I was reminded that the lens technology is constantly improving still. The lens quality is particularly important when you are using a 45MP camera. At this "film" resolution, the lens, rather than the film, can become limiting. Using my good old Ai Nikkor 20mm f/3.5, I can see that the lens resolution is becoming a bottleneck in the overall final outcome.
So to sum up, my impression of the Z7 is: It is a good pro camera. I would recommend getting the Z7 instead of the D850, UNLESS your field requires fast-AF shooting, like sport and wild life, in which case the D5 is the best, but the D850 (with a battery grip) comes so close, with 45MP. For the majority of photographers using or thinking about the D850, the Z7 is as good or better than the D850. The Z7 is the future; DSLRs are a legacy (you do have 10 years left though).