I think usb load is banned but I'm not positive. I'm not a GC runner there are others who can tell you for sure about this

Hi, for gamecube it's forbidden to use an USB Loader as it might influence the loading time. So you have to play using a legit copy of the game, which you can purchase easily with a memory card.

I strongly advise to purchase a PAL copy and check if you can properly run pal gamecubes at 60 htz on your minotor screen. Pal is the fastest version