I was about to get the Nikon Z8, but the new canon Eos R6MIII is awesome too. I do wildlife, both video and stills are important for me. Also being a canon user would mean being able to own the 200-800.

What are your thoughts?

Hey guys I'm looking for thoughts on switching from the Canon R6II + 100-500 to the Nikon Z8 + AF-S 200-500. I spent around $5000 on the Canon system as a whole (r6ii $2500 and 100-500 $2700) and would want to keep the budget around there. That means that a new Z8 paired with a used F 200-500 FtoZ would be in that range and would give me zero rolling shutter and significantly more MP for cropping.

I originally started out with a Nikon 5600 and Sigma 150-600 C and have some other Nikon F lenses lying around like the AFP 70-300 FX and AFS 50 1.8 though I have been trying to sell those. I found the 150-600 to be clunky and often times found the autofocus and stabilization lacking, at times I would also have some issues with connectivity with the Nikon body. Maybe this is just a poor copy but I think I would prefer to stick to native glass if I can in the future. I moved to mirrorless because I also wanted faster framerates, full frame and electronic for landscape, AI autofocus. I would have gone to Nikon mirrorless but based on reviews their animal autofocus was way behind Canon and Sony. I went Canon over Sony A74+200-600 for the faster 4x frame rates and additional body features (rolling shutter, bracketing etc).

Since moving to RF 100-500 I've found the lens to be much lighter, faster autofocus and significantly sharper. However I'm still bothered by the price and the loss of 2/3 - 1/3 stop of light compared to competition, the design also does not pair well with the teleconverter. The loss of light isn't a huge deal as I've found that I can get somewhat acceptable images even at max iso 25600 (with D5600 I would max at 3200) but I would really like that wider aperture for the creamier background rendering. I think moving from APSC to Fullframe I might have underestimated the change in field of view and would appreciate the extra ability to crop. I like the Nikon wildlife lens options more but truthfully most of the Z series are actually more expensive than the RF100-500 so while I would like to have the ability in the future to grow into them I'm not sure I would purchase a 4k+ lens. I'm wondering that the performance of the adapted lens are with a Z8 or Z9, I expect a hit to the tracking. Though with my Canon kit the AI tracking is said to be one of the best but still has a lot of issues with grass, the ground and twigs anyways so I'm not sure if I will find a difference I will care about. I hear that stabilization with the Z8 and Z9 is amazing but I don't know if that's only with Z lenses.

Sorry for the text wall but TLDR: If you were to start wildlife shooting would you go with the Canon R6II + RF 100-500 or the new Z8 + 200-500 + FtoZ adaptor?