According to the Canon MTF charts the RF 800mm f/11 and RF 100-500mm + 1.4xTC @ 700mm are nearly identical. This means the 800mm should outresolve the 700mm because of the extra 100mm. I find this with my copies. Others have reported the opposite. It could be that I have a poorer copy of the 1.4x (and I have never been that happy with it) and a good copy of the 800/11. Others might have vice versa. So, I am interested in others experiences.