I've fitted my 8600gts with a HR-03 GT
Can OC stable to 747/1160 from 675/1008.
Temps are only 51 max but cant oc igher without artifacts.
Why have I heard of people oc'ing higher with watercooling when my temps clearly aren't a problem?
Do I need to volt mod?

well i got a 7600GS stock 400/500 OC 600/750 stock cooler... temps r fine but artifacts at 650/750 or 600/800 so....im happy with the 50% increase LOL and i leave it be...

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.

Sorry missed that yours was a GTS, but same thing should apply to your card except you have faster ram, not sure but betting the gpu are exactly the same and the results aren't going to get much better beyond what you already have it clocked to.

Saw some guy say he got his sli'd 8600gts's to 820 core???
kk TY gonna read some guide on bios editing.

Think i read same article, because of 6 pin on gts version he was able to up volts more, for a higher clock.
Wonder what he was using to keep it cool

Water cooling...