GEwart wrote:
I sympathize with your dilemma. I reluctantly purchased an EOS R with the kit 24-105 STM lens and the 800mm f11STM. Not a cheap purchase for me at all. I'd read all the dire warnings about the unsuitability of the R for wildlife. I can't pursuade you to go for the R, your best route as already recommended here would probably be to hire an R6 for your once in a lifetime shoot.
My experience with the R so far has been positive, as a hobbyist I can live with the slow framerate and the tracking autofocus seems very good when I take the occasional BIF. The R and 800mm f11 may seem to be a nightmare combo for BIF but it's not too bad for me, with good fieldcraft it can work. With the 30mp sensor I can crop quite generously and the high iso performance seems excellent to me. I haven't noticed the blackout on continuous shooting but I never take more than a dozen frames at one time.
I had a 7D2 a number of years back with a Tamron 150-600, whether or not it was user error or because of the third party lens I only very occasionally nailed BIF shots with it. I wasn't impressed at all with high iso performance either.
All pictures here with the EOS R and 800mm f11 STM handheld:




iso 12800
No doubt the R can get nice photos as you well demonstrated. I certainly got plenty of good photos with mine. However, if I’m spending that much on a camera I am really looking for one that makes my job as easy as possible. I do enjoy a challenge and got tons of great in flight shots with my original Digital Rebel but it’s not the camera I’d recommend to someone who is looking for a tool to photograph a once in a lifetime wildlife opportunity.