When playing single note lines(alternate picking, sweep picking) on a strat( 3 single coils) with a loose fist grip, i.e PAul Gilbert, is the pick in between the middle and neck pick ups or the middle and back pickup, or where? Thanks guys!

I think it doesn't matter where it is, as long as you're comfortable. Mine's mostly slightly towards the the left of the middle pickup.

If you're a tone junkie, you might also want to find a place where you can get that tone where you want, because depending on where you pick, the tone will be different. For example, if you're picking really close to the bridge, you get a more twangy sound.