There's a certain argument to be made about the type of pick you use too.
A softer pick will tend to flop around more the faster you pick making it hard to consistently aim at the string. A hard pick will stay rigid.
I know as soon as I switched to a smaller, thicker pick that my speed picking increased. However, I lost a lot of feel because I couldn't clench up on the pick and bend it a little during slower parts and playing rhythm.

So after a lot of time I got to the point where I use both now. I keep them handy on a mic stand or something. During rhythm parts I'll use a .60mm nylon pick. Then I toss that away and quickly pick up a small, hard 1.0mm pick for the lead and vise versa.
(...of course by the time you've finished there are picks all over the floor but hey :)