For slow playing , I don't think the way you pick realy matters technicaly , although different picking styles give different tones & attacks.

For playing fast , the main objective is having a less motion , that's why you should develope finger (the fingers holding the pick) movement ,wrist movement , and very slight elbow movement if necessary.

Guitarists who have impressive picking techniques (IMHO) are Malmsteen , Petrucci & Michael Angelo .