Disabling External Frame Buffer impacts performance?

[Falco1211]

Hey guys, so i wanted to have the GameCube intro in Dolphin, i made it work but it was glitchy, then Dolphin Wiki advised me to disable XFB (External Frame Buffer) and disabling it made it work perfectly, but i've noticed that Mario Galaxy 2 was having some slow downs, so does this XFB thing really impacts performance? I'm playing at 720P (Internal Resolution) and upscaled to 1080P (my monitor's native resolution) Thanks for the help guys