My husband is 6' 5.5" tall, and he can ride everything, but Mulholland Madness is VERY uncomfortable for him. He manages to fold himself in somehow so he can still ride it though - LOL!
However, I made him stop riding the rides with his hands in the air on Space Mountain and Big Thunder Mountain because I'm telling you, with him being so tall, and add to that his long arms/hands/fingers stretched high over his head, there's hardly an inch of space between his hands and the ride structures at certain points in the rides, and I'm afraid he'll lose a hand or finger or something.