When you listen to Mr cucumber, it sounds like some mickey mouse high speed licks. The guy has some kind of syndrome that makes his muscles hyperactive. As for the 20 notes per second, it's true that it's really difficult to go way faster, unless your practice routine is only based on speed. I think that over 25 notes per second, you must have some kind of physical or genetical gift. Actually, I have tried to play this fast because that's what I hear in my head.