Hi Kiarash,

There's not going to be only a single solution here that will solve all problems. The best way is going to be learning various picking strokes / hand positions. Much like a drummer learns combinations of stick control with fingers, wrist, arm for different applications.

Michaelangelo Batio is an extremely fast metal picker and he plants his picking hand pinky and ring finger on the body of the guitar. He swears by it (or at least he did in his old videos). The drawback for him (which he may not admit to) is that he's using almost entirely bicep and shoulder which, at a slower tempo, isn't efficient at all. And also hard to control! At slower and normal speeds the picking stroke needs to switch over to wrist and forearm twist.

The other problem is that when he is playing so fast with his bicep and shoulder, he's actually not picking accurately -- he's missing a ton of notes, but it's so fast it all becomes a blur. It goes in and out of sync. He might go up a scale and pick C D E E F G G A B etc, hitting some notes more than once because the right hand is hard to control when picking like that.

Then there are players like Paul Gilbert who are entirely wrist and forearm but can also pick quite fast and with total control and staying in sync. (There's always going to be some complimentary finger-flexing as well).

I would just watch videos of your favorite extreme speed players and try to figure out what is working for them (which muscles are they using? Bicep, shoulder, wrist, fingers, some combination), and then what will work for you. It's going to be different for everyone.

AND it's going to be different for different situations / tempos. See them all as useful tools and be able to grab the one you need. Hope that helps.

-Carl.