Where do you read that the AF speed of the R5/6 is better than the Z6/7? I am not saying it isn't, it's just that I haven't read anything either way. It seems to me that AF speed has pretty much plateaued across most higher end bodies with the latest lenses - I just don't recall the last time I read "the X lens focuses faster with this Y body than this Z body"
By chance I just read this:
http://www.naturalart.ca/voice/blog.html
6. Lens Performance: Autofocus.
Because autofocus performance is dependent on BOTH the AF performance of the camera lens AND the camera body in use, and because at this point in time the AF speed and responsiveness of Nikon's Z-series cameras lags considerably behind their top DSLR's,
But he is mixing AF "performance" and AF speed.
I read Thom's review:
https://www.zsystemuser.com/z-mount-cameras/nikon-z-camera-reviews/nikon-z6-camera-review.html
It specifically address AF
speed (my underline added below)
The main worry of Nikon DSLR users considering a Z6 has tended to be focus speed. They needn't have worried. Phase detect is essentially instant—okay, there's lag in the electronics stream to account for, but that's minimal—so it really depends upon the performance of the focus motor in the lens as to whether the actual focus speed is good or not. The worry among DSLR users was that no other mirrorless camera with adapter has managed to achieve reasonable focus speed with existing F-mount Nikkors...................I see no tangible difference in how AF-S lenses on the FTZ adapter work (yeah, a confusion of terms, that's not single servo, but a lens motor designation). I actually think AF-P lenses may work a little faster on the Z6 than they do on the DSLRs, but that "little" is so little that I can't really measure it, and you have an apples and oranges problem to deal with even trying to do such a test. Suffice it to say that Nikon DSLR AF-I, AF-S, and AF-P autofocus lenses mounted on an FTZ adapter pretty much keep their performance characteristics on the Z6.
So I stand by my point that the AF
speed with the Z70-200 does not seem to me to be waiting for a better body. Yes, overall AF performance (tracking especially I guess) will need better firmware and/or a better body. But that will apply to any lens, not specifically this one.