there are several ways to play fast,and unlike some others,i dont think they all play the same fast stuff.
Eric Johnson plays extremely fast difficult pentatonics runs,arpegios,string skipping licks using up picking that maybe not many people notice it.But he never forgets the melodies.

Joe Satriani;Plays very fast licks using a lot of combinations of 2 pents boxes put together,with one picking maybe 2 in groups of 6,8,10.. notes that'll make you stretch your fingers for 5,6,7 frets if he's playing arpeggios in one string.You gotta have a lot of strength and endurance to play 2 hours like that and make your fingers fly and look easy using gauge 10.

Shawn Lane:Similar to Eric Johnson in usage of Pentatonics,but a little different way of play them,using a lot of leggato,throwing diminished,and augmented intervals(the hardest interval to play)speacially fast as he played.In my opinion the guy that played the hardest things fast than anybody else,but not melodic,only in some occasions.

Buckethead.He plays just about anything,any variation extremely fast including the augmented intervals,sweep picking with his mid finger using the first finger to tap,and evrything else i guess.Nowadays he is the fastest guitar player that can play beautyful music and use well the techinique.

John Petrucci.Vey fast using his right hand to pick several times the same note(his trademark),also plays very fast minor 3rds,major 3rds but nothing that is really impossible to play.You can get there only focusing on John's exercises.

Michael Angelo.Extremely fast using arpeggios and minor3rds and major 3rds as well.
Paul Gilbert.Extremely fast playing arps with alternating picking,minor 3rds and maj 3rds,pentatonics,using tapping

And the list go on and on.Of course Malmsteen there too,but the bottom line is :you dont need to be one of them to create great music!!
Just think about that!!!!