I did a lot of research buying into the Canon R system for wildlife photography. I wanted the RF200-800 lens and the best camera that I could afford for it, which for me is the R6 Mark II. Because of the full frame sized sensor AND less megapixels on that sensor that the R7 has on it's APC-S sensor, the pixel are larger and thus gather more light. Therefore the sensor is much more sensitive to lower light, which is a big deal in wildlife photography. The 200-800 is not a fast lens, but the low light ability of the R6 Mark II really helps with that. As an example this morning was very overcast and gloomy.. I shot these Hooded Mergansers from about 80-100 yards, 1/1000. F9, ISO 16000. I have increased the exposure a little and used noise reduction in Lightroom, but I'm not sure I would get that picture without the lower light ability of the camera. I think it may have been darker and possibly less sharp with the R7, I can't say for sure never having used an R7 but pixel size does make a difference in light gathering.
