So, we WANT the full-frame FOV, thin DOF, lower noise, etc at times. But we also want reach for wildlife. They two separate issues. The 70-300L is nice, but definitely has it's limits.

Further digging reveals it's commonly believed that the EF 100-400 II doesn't resolve enough to add any detail with a 1.4x over just cropping the bare lens with used on a crop body... so I'd really only get 400mm usable reach anyway. (640mm equiv.), it would just be softer and need more downsampling with the 1.4x.

On the other hand, the RF 100-500 DOES resolve extra detail. Adding the 1.4x makes it 300-700mm. If I went all out and got both an R8 and an R7, I'd have an effective reach of 1120mm, more than double my current 300 (effective 480), plus 50% more pixels... that's a lot of reach.