Blasting - Motion once told me the best way he found of building up endurance is to play reign in blood all the way through with blastbeats at every avaliable opportunity.
and the gravity blast bit you wrote is pretty much spot on. I hold the stick the same as I would normally but turn my hand parallel to the snare and let go with my thumb, holding it with 4 fingers, it seems more comfortable to do it that way at speed, the way you described is perfectly adequate too though.