yeah. HyperThreading rules for games. i remember on my Celeron 1.2 (yes, i know, 1.2GHz ESPECIALLY in a celeron ain't much to begin with) whenever i minimized a game, it would take a few minutes for my desktop to show up if it was a heavily graphical game like UT2k3 or somethin like that. now it only takes a couple seconds to a minute at most.
i think changing priority won't have that kind of effect. not sure though.