my left hand speed sucks for lead/shred. i can barely do it.
my right hand is VERY fast, and my left hand can keep up for riffs, but not shred. i use my speed for fast riffs, like thrash classics such as Creeping Death, Master of Puppets, Raining Blood etc. and my hands play in perfect synchronization, but when it comes to soloing, i just physically can't do it. in fact, i gave up the other day, and decided i was going to be an uber rhythm guitarist. it's just what i'm wayyy best at.
BM