You are probably thinking of the USB loader for GC games, the original Dios Mios which could only (barely) run a handful of games and even those had severe issues because you have to disable ARAM support for USB access to work.
The only "fast paced" games I've played are burnout 1 and 2 and extreme g 3. They played fine, aside from the audio streaming. I'll try fzero and see if I have any issues.Edit: I just ran through the ruby cup with no issues. The title screen music was stuttering a little, but it didn't affect the main game at all.