500 watt psu is easily enough for your setup, if anything I would have said to lower the overclocking on your CPU a small amount, more that likely i would say that your voltages arnt suitable on the overclock you have. I havnt looked too much into it but generally i would say thats the issue.
On another note, what games do you get poor performance and also what settings are they at.
Deffinatly update to latest drivers on your graphics card, if you are on the latest try rolling them back to a previous lot. Generally poor game performance dependant on the type of performance dip your getting would indicate to graphics drivers, its the usual culprit anyways.
If none of that helps, please link in your temps during 3dmark just to check for any heat related issues.