Well, its terribly hard to tell without seeing and hearing you play, but from the grounding you have I dont see that you (or brow) would have a problem.
Not that I'm much of a shredder, but machine gun riffing (BFMV?!?!?!? Yeah, right - start with, say, old metallica and fear factory and we'll go from there!!) is a strong suit of mine (such that I have any) and you need to be loose and relaxed to do it - firm pick attack is need, but tensing and cramping up your motion is the enemy. Quite solid, but not hard, grip of the pick and relaxed, smooth motions, which dont need to be too short, you have room to move between the strings, they need to be
controlled and precise, which doesnt automatically mean short motions - some width to a pick stroke, I find, helps keep notes clear and delinieated; your picking can start tripping over itself a little if you keep the motions too constrained (though it seems to work for some) and again, relaxed (or at least not tense) is much better, for most (kerry king pretty much beats the cr@p out of strings with a motion from the elbow, so, y'know, whatever works).
That said, theres no one exact style. Here are a few high quality examples of (and one very poor example of, for levity sake) fast rhythm picking of varying degrees of complexity.
meshuggah doing bleed. This aint that easy, work up to it (if youre interested in doing so); its way beyond BFMV
http://www.youtube.com/watch?v=bd6z39PbIRwThe vid for origin, finite - the fella with the jackson warrior (paul ryan) has quite a wide, loose picking style, but its very precise
http://www.youtube.com/watch?v=MIMW0aHN0ksThis vid is a pretty cr@p representation of them, but karl and dallas from nile use totally different picking techniques to play very fast rhythm (karl uses very narrow motions, dallas a much wider, harder, more violent pick attack that sort of goes against the usual wisdom of keeping relaxed)
http://www.youtube.com/watch?v=KDpw-Med3dwDino doing some divine heresy.
http://www.youtube.com/watch?v=DBgti_gyVQQAnd lastly hetfield showing the harder style (but still pretty relaxed, just more forceful, if that makes any sense) that makes metallica rhythm what it is (and hammet failing dismally to pick up a simple riff :lol: )
http://www.youtube.com/watch?v=546KjKMB9kwMaybe some of these examples will help you find a way to play the rhythm that you want to play in a way that works for you?
Shredding....there are probably better people here to advise than I (not that theres no one better to advise on metal rhythm :lol: I just know that moderately well is all).