Set the affinity for the game to a single core (or alternately try installing AMD's Dual Core Optimizer). I get the same kind of timing issues in Unreal/UT on my Opty 170 (though with the Optimizer they seem to be fixed).
Also, the original Unreal engine doesn't seem to handle framerates over about 200+fps very well, so the gamespeed increases a lot once you surpass that frame rate. Simple fix for that issue is to use Vsync (and ideally Triple Buffering along with it, though you're not likely to find many situations in either of those games when you'd drop below 60fps anymore...)