Jeff, you have rekindled my interest in the 800/11. Today I tried it on some gulls. They were shot from home and they were very close indeed. It was hard locking on to them, but not as hard as I thought it would be. I came away with a great many good shots. Most are already deleted, but here are two that I particularly like.
It's truly amazing I managed to lock focus on them, mid flight, from such a close distance.
Lost the wing tip there. Yes, full frame shot.
Canon EOS R5m2 . RF800mm f11 IS STM . F/11 . 800mm . 1/3200s . ISO 2500
This one was really close, lost both wing tips and decided to crop in a bit more.
Canon EOS R5m2 . RF800mm f11 IS STM . f/11 . 800mm . 1/3200 . ISO 1000