My core doesn't go too far, but I wonder if that is a heat issue. The memory is default at 800, i'd go to 1.1 or 1Ghz, it goes there fine. (it has that samsung 2ns memory). I'd wait to get a 3rd party cooler. There might be one designed for the 6600GT AGP, at least hopefully. The AGP bridge chip gets extremely hot with just that heatsink. PS, the more i look at your rig, the weirder it is, you have almost the exact same setup, down to the speakers LOL.