If your able to flash your bios, u can set the 3d voltage to 1.35v rather then using a pencil!
Pretty sure the card does this anyway by default switching to 1.35v, but you can override stock settings in the bios, by using nibitor 4.1 bios editor, nvflash, and a usb bootable drive or floppy.
I flashed 2 xfx 8600gt's to 720/core, 850/mem (my ram was kinda touchy beyond that)
Mine was solid at 745/850 but got close to 65-70c/load, so i went with 720/850 speed, never over 50c/load at this speed.
Some mobos give you an option in bios, to up the volts on your pci-e slot. I also did that, with noticeable results (got me to 750 core).
I haven't used this card in about 3 months, so hate to make any quotes on those settings.
The lack of a 6 pin powersupply is this cards only drawback, but for low end gaming pc's that just need upgrade from onboard graphics, this is still a great card because of the lack of the 6 pin.
These cards have poor cooling and need a good airflow to do any kinda OC, recommend buying better heatsinks if u must go past 720 core speeds.