I asked a question about this a while ago but didnt get round to doing it yet…
i’ve gotta Geforce3 Ti200 and want to overclock it…
i have 3dMarkas well, so i can see what improvement i get, but what i wanna know is how do u know when your getting near the limit of “safe overclocking”
do u?
-look at the temperature? (if so what is too high)
-play 3d games and if it crashes its too high?
-…
also should one overclock the main speed and the memory seperatly or together a notch at a time?
My advice is to leave it. Sure, it is possible to overclock the card slightly for a very modest improvement, but its just not worth the hassle. Lots of work, little gain, and you already have a high end card. Why bother?
I usually overclock a little, more because I can than anything else. It’s really not a dramatic performance boost compared to overclocking your processor.
Basically, go one notch at a time in very small increments…do the core and memory separately to minimize confusion. After every time you increment, do a stress test, such as 3 or 4 runs through 3dmark 2000 or run a benchmark demo on some demanding 3d game (like UT2k3, for instance). Keep going until you start to see artifacting (the screen starts to wig out in some obvious, unprecedented way). Then set the card back a notch or two and give it time to cool down. Keep it at that setting.
It’s really <sarcasm>…exciting…</sarcasm>. But if you absolutely, positively have to raise your framerate from 83 fps to 85…go for it. 
Using 3DMark 2001SE, disable title screens between tests, and loop the Vertex Shader test to test your memory. If you see ANY graphical corruption or anomalies (such as arms or heads being stretched out accross the screen), abort the test and reduce the clock speed. If you see no errors after 25 loops of this test, you can consider the memory to be stable, and try increasing the clock speed a little more.
To test the core speed, loop the High Polygon Count (8-Lights) test. The test will hardlock your system if your GPU is clocked beyond its capabilities. If your videocard withstands 25 loops without crashing, you may consider it stable.
I’d suggest you overclock the memory first, then set it back to normal and overclock the GPU. When you have determined the limits of both the memory and the GPU, then set them to the max together and test using the entire 3DMark suite. You can usually loop each test 10 times or so for preliminary testing, increase to 25 when you think its stable for the final test.
Hmm? There’s not much work involved in most video cards these days - it’s generally just a switch to flip and a slider to move in the driver settings.
And the improvements can be fairly dramatic. My geforce 4 ti4200 is just as fast as any ti4600 core on the market, and the memory is about as fast as a ti4400. Basically, I got “free” almost 4600 card for the cost of a 4200.
Oh - and artifacting or locking up is the dead give away. Any ‘tears’ through the screen or weird ‘popping’ and that sort of stuff is a good sign you went too high.