Sorry if this is has already been solved, (I have gone through many pages looking for it) but I'm overclocking my GTX 560, and I've reached 950MHz on stock voltages.
I want to increase the core clock further, and temperatures aren't a problem at the moment, but I'd like to know how much to increase the voltage by to keep increasing the core clock (it's at 975mV at the moment), and how much is safe.
More advanced users push the frequency often way higher. Usually when your 3D graphics start to show artifacts such as white dots ("snow"), you should back down 10-15 MHz and leave it at that. Usually when you are overclocking too hard, it'll start to show artifacts, empty polygons or it will even freeze. Carefully find that limit and then back down at least 20 MHz from the moment you notice an artifact. Look carefully and observe well.