Thanks for the reply. There are not a lot of photographers in my neighborhood ( me and one other ) so my chances of a hands-on session with the Z6 are pretty slim. I enjoyed all 43 pages of this thread though, and many of the images are pretty impressive, yours included. I'm loath to give up on the mk ii, as its stabilization is awesome and its paid for! But those images, especially the clean low light ones make me wonder if I'm missing a good thing. Ian, on your telephotos, how many stops do you think your VR gives?
It sounds like the C-AF might be similar with both post firmware cameras, although my gist from reading the posts here leaves me feeling that the Z6 might focus better, but the evf blackout hinders the process. I still have a slight blackout issue with the Oly, but I'm used to it, having never shot a DSLR.
I'm still enjoying the Mk ii and it can produce some good images with decent light. I still have a lot of misses with C-AF when shooting BIFs and I'm getting pretty good at following them in flight. Firmware 3.0 has helped though.
I'm not certain about the efficacy of IBIS on telephotos, because Nikon doesn't use a Dual/Sync IS. IBIS only works on lenses that don't have VR, and all of the telephoto lenses I own have VR (as does the 500/5.6 PF you're interested in). What I can say is that I've never thought to myself "Gee, I wish the VR were better on my 70-200/2.8 or 300/2.8". The lens-based VR works very well for telephoto optics, and with my 85/1.4 I can easily shoot at 1/10, equating to 3 stops of efficacy. I could push it further, but for what I shoot (and how good the camera handles ISO), there is no need.
It took a bit of getting used to, but I really don't pay much attention to ISO anymore because the camera is so good. With my E-M1 II, I was always trying to keep it as low as possible, but with the Z6 that's not really an issue.
I would highly recommend you rent a Z6 and 500/5.6 PF (or another telephoto) to see first hand how the EVF blackout would affect your type of shooting. For some it is a non-issue, and for others it may be a deal breaker. I'd rather spend a few hundred bucks on a weekend rental to find out, rather than spending $5k buying the gear only to realize the issue after you've made the purchase.