Vista or Win 7? Being dual core that could cause I/O blocking on the FSB. Also make sure you are running the latest nvidia drivers. One last thing, Always make sure you are running the GPU in high power mode. If the A/C adapter comes out, it will force the Nvidia into low power more (Unless you override it which you may want to do).
Hope that helps. I have the Asus G73J with the ATI 5800 series and the 1.6/2.3Ghz intel i7 and it runs great unless the A/C adapter falls out...lol. Then I know.