Having this be the biggest struggle in my guitar playing wanted to get your input.
I usually pick with my wrist; however for anything over say 150 bpm 16th notes I end up using an arm / wrist combination. I'm never tense when I do it, and i have really good control with it.
However for the life of me i can't under stand why I can't move my wrist any faster and why I have to end up using my arm to get faster speeds.
Having just watched this video I see Chris Broderick went through a similar change; however he doesn't really go too much into how he did it.
YouTube - Chris Broderick (Megadeth) - June 2010 Lesson
Would love to get your input as far as a good way to move to a wrist only technique.
Most guys I've seen with really developed picking techniques seem to use a combination of wrist and arm, where it's (I'd say) about 70% wrist and 30% arm at top speeds, where it's a kind of 'whipping' motion...
The stigma attached to using your arm muscles when picking at high speeds is mostly due to it often being a result of tensing up your whole arm when trying to reach speeds your not really ready for.
I'd say, provided you're staying relaxed, I wouldn't fret too much about it.