Just because something benchmarks well doesn't mean it's going to perform that well under every environment. Software-hardware intercompatibility can always cause variations. All I can say is grad the newest drivers for your video and sound cards, drivers for your moterboard, disable unnecessary programs (virus scanners, DC projects, popup blockers, ram refreshers, etc.), get the latest version of DirectX, and try lowering resolution. If all of that doesn't work there's some optional OS optimization I could help you with, but it could just be that BD doesn't like your card completely.
