My guitar friends and I had suspected that Buckethead is actually Paul Gilbert (of Racer X and Mr. Big fame) in disguise. Paul Gilbert can do some of that stuff too. Shawn Lane is an underground guitar player who was phenomenal (but he passed away a few years ago). He was super fast with alternate picking and had great legato technique also, and was a great composer (his Powers of Ten album). In terms of pure speed alternate picking wise, Rusty Cooley is damn scary.