Watch the temps on the card first. put it in, fire up Everest and log the temps in the back ground as it plays a game or a graphics benchmarking tool. if you need a copy of everest I have one cracked. Leave the fan controll on auto and see what it does out of the box. on air I would want to see more than 75C for a stable nVidia card. I say nvidia card becasue they seem more heat sensitive as far as stability goes.
Then do another benchmark test with the fan controll on manuall 100%. not the differences.
Over clocking is a process where you bump the core speed, shader speeds & memory speeds up on the GPU a little at a time and test for stability. I use 3dMark 06 to test. if it completes without error or hanging, it will give you a score and some FPS information. then I slowly bump the core up until it fails or freezes or artifacts the video play back. document the speeds each time in excel… pass/fail ave FPS per test, test score, and max temp recorded.
once it fails, I go back to stock clocks and then repeat the process on the memory speeds. go until it fails, document everything and roll it back.
repeat processes ont he shader.
once you find the roof for each component on the card cranked up and running stable, I usually set all 3 to about 85% of the max value for each. you will never get a card to run stable with all three cranked to THEIR max. then if it passes at all three set at about 85% of their max values I found in the beginning, I slowly bump them up all at the same time, until it fails. then bump them back to the last known good and retest for stability again. Then its a cat and mouse game to adjust one then the other and find the best combo of settings.
document everything, and you will see the trend while you overclock, that way you can go back and find landmarks to work from when all hell breaks loose.
There are some very noticable gains from doing this. just watch your temps. you might be “stable” at a higher overclock, but prolonged use at high clocks and high temps will kill the card quicker.
My liquid cooled GTX285 started life out at 648Mhz Core, 1476mhz Shader & 2322mhz memory. They sell an overclocked one that hits 666mhz and what ever the shader and memory is. I maxed it out around 800mhz, 1800 shader, and 2600 memory… IRC, and it didnt break a sweat above 45C!!! It have been running like that for many months now, and my proc is running 4.55ghz on water too. took about 4 weeks of work to get them there but its retardedly fast and 100% stable.