I find it easy to go up in pitch really fast because I can use hammer-ons and also because I am able to coordinate my left and right hands easily when I am going up for when I play legato style.. coming back down is where I really suck.. so if you listen to any of my stuff you will see I tend not to come down as fast as I go up. I'm working on it though and when I am in the right mood and relaxed I can actually play just as fast going back down again.. it's just a matter of practise and being in the right frame of mind, and that frame of mind also comes from practise and experience.