Does i7 Overclocking Have to Be Done in Certain Units?

I have read that overclocking needs to be done in specific increments. For example, you can overclock a 920 by 750 MHz and achieve good results, but if you would to overclock it by more -- say by 800 MHz or 900 MHz -- your performance would actually be worse than if you had stayed at 750 MHz overclocking. The next "proper" overclocking level would be by 1.5 GHZ (2 x 750 MHz), although there are obvious heat and other issues at that speed. The key point is that overclocks between 750 MHz and 1.5 GHz would either be less product or counterproductive to simply overclocking at 750 MHz. Anyone know anything about this? Thank you.