I shoot almost exclusively wildlife in Europe, so the animals, especially mammals, are rather shy usually. My current setup is a 90D with a Tamron 150-600 G2. I also have the Tamron TC-X14 that I almost never use, because I usually have enough reach with 960mm equivalent on FF already and the teleconverter in combination with the high pixel density of the APS-C sensor doesn't allow for really sharp images in my experience. I also have a Tamron 15-30 G2 and a Tamron 24-70 G2, they don't get used that often right now.

My thought process is that the go-to upgrade would be the R7 as I am used to the reach of an APS-C sensor and it is mainly targeted at wildlife shooters. However, the R6 II is the better camera overall, it has more fps, less rolling shutter, a bigger buffer, arguably better AF although that won't matter much as both will feel amazing coming from a DSLR, but it has less reach being full frame. I know many pro European wildlife photographers are using FF but usually with big primes and teleconverters that I can't afford. I would use my good ol' Tamron 150-600 G2. On FF it would probably have enough resolving capabilites to use the 1.4x teleconverter I already have, especially because the R6 II only has 24MP. I would get almost the same reach as now: 960mm on APS-C vs 840mm on FF. Probably similar or even better sharpness on FF as the high MP APS-C sensor is quite demanding. Cropping a lot doesn't matter that much, as the best pictures are taken when animals are close and not 100m/330ft away anyways and I don't print large. I would be pushed to try to get closer with FF, probably resulting in better pictures overall. If I went with the R7 I would probably get the RF 100-500 in the long run due to better sharpness, resulting in less reach. Another small benefit of fullframe could be that I might enjoy using my 15-30 and 24-70 again as they would get more FOV for landscape and smoother bokeh. Now my questions: Is there anything I am missing? Is one of the cameras clearly a better choice? Are 600mm on FF obviously too short for mammals like foxes and roe deer? Is there a difference concerning AF between DSLRs and DSLMs that allows for sharper images, meaning the Tamron is good enough for the demanding 32MP APS-C sensor? Does anyone have experiences with the R7 and/or R6 II and the Tamron 150-600 G2 (maybe even with the Tamron TC-X14 as well)?