1) double-check that your RAM has not also been overclocked (either in BIOS or Memtest)
2) run Memtest any time you change CPU or RAM settings
3) Overclocking and gaming:
With a high-end CPU, usually the graphics card becomes a bottleneck (or you are synched to 60Hz and your hardware is bottlenecked at no point).
Even with a GTX680 there are very few games that would benefit in the slightest from a CPU overclock. I have a lowly i7-860 and only a handful of games benefit from an overclock.
However, when you overclock the CPU not only do you also create a lot more heat, but power saving features are often disabled so even in IDLE mode the PC is noisier.
4) New GPU's and HEAT:
*With the new Kepler GPU Boost feature (AMD has own version in HD7970 GHz edition and future AMD cards) the GPU will slightly adjust its performance based on the temperature.
If you overclock your main CPU and add heat to the case, it's actually possible to LOWER the performance of a game slightly. Probably not by much. However, more heat, more noise and possibly slightly lower performance in some games is a lose-lose-lose situation.
I believe your CPU has HT available. It won't benefit any games at all. I know Spider-Man Web of Shadows won't work with it, BF3 I think has been fixed and for most of them it doesn't matter either way. I think it slightly affects overclocking but not by much. I've only seen it actually benefit me using Handbrake (depending on settings) and Acronis True Image (compressing my backup). If you overclock you may wish to investigate if HT affects that in the slightest on your CPU.
- investigate if overclocking actually BENEFITS YOU (if not, don't)
- make sure RAM is not overclocked (if it is, you may need to drop the RAM Multiplier in BIOS)