#1
so, ive never been a lead guitar player, or a very proficient shredder. but lately i have been working on it. right now im working on the solo for "Two Weeks" by All That Remains.

my question is...
what would be a better picking position to have while shredding, excluding sweeps and legato, would it be better to have my pick in the vertical position like i would for trem picking, or horizontal like i would use for just about everything else?

sorry if this is worded kinda weird. its sort of hard thing to explain without showing someone.
#2
Your trem picking technique should be the same as your normal alt. picking technique. Anyway, the exact angle depends on your preference and hand position, but usually an angle 20-45 degrees from the string is preferred. Check out this Paul Gilbert vid http://www.youtube.com/watch?v=s-NOMn3P9AE
#3
Angling is more of a choice for the kind of sound I want. If I want it a bit scratchier sounding then I use it, if not I don't.
Angling can help a little with fast picking (at first), since the slight angle means there is a little less resistance when hitting the strings. Over time, I've found that I can pick equally fast regardless of whether I angle the pick.
The biggest thing is how you pick (rather than whether the pick is at an angle) - small, efficient movements, and just the right amount of pressure - in most cases (like when executing a fast run), the pick should feel "firm" - not a death grip, but not bouncing around from contact with the strings either.

And +1 to what which ones pink said - normal alt picking and trem picking are the same from a picking hand perspective,