Keep in mind your PSU can't support a 670 and an overclocked i5 2500K. The PSU in my build would allow for Crossfire/SLI of the 7950 and you'd get a motherboard supporting 8x/8x with an easier to work with for factor.
Your editing, you'll need 8GB as well so my build has that going for you as well.
All overclocking is safe. A common misconception is that it degrades the life of your CPU/GPU/hardware. That is TRUE but not to the degree its been made out to be. At most the degradation would still give your hardware a 5-7 year life AT LEAST. You would probably upgrade before then.