Just out of my own curiosity and in case anyone else might be interested, I took these today as a sort of demo to show what images are like at 1200mm and 1920mm (field of view equivalent) using a 600mm f/4 lens with a 2X converter and the 1.6 Crop mode of the R5.

These images were converted from RAW in DPP4 and with no adjustments sent to photoshop where I added the text. They are uncropped images. The only processing performed was Topaz Denoise AI, although they looked really good without it, to make the background somewhat smoother.