Thanks Louis for your comment about the hummingbird!
I have rented the XF 150-600mm lens for four days. It is too heavy and bulky for me to carry about and use handheld for any duration
in the way I prefer. It can take sharp photos in good light, but the f/8 at 600 is a limiting factor. The Northern Cardinal photo is the best example from one of two short series I took on the same day, this taken earlier in the day with good sunlight and cropped. The focal length is 405.6mm (=600mm FF) at f/7.1, ISO 6400, 1/400 second.
The upshot is that I am going back to MFT, basically because of weight and size considerations. I anticipate trading back for the OM-1 with the Olympus 100-400mm lens. The second photo of a Northern Mockingbird was using the E-M5 Mark III and Panasonic Leica 100-400mm lens that I used to have. The focal length is 350mm (=700mm FF) at f/5.9, ISO 1600, 1/640 second. It was cropped about the same amount.
View attachment 197564
View attachment 197565