I don't know how knowledgeable these forums tend to be on matters of overclocking, but hopefully someone can help me figure this out.
Just built a new PC, important specs for my question being: i5 3570k; XFX 6870; Corsair CX 500W.
I thought 500W would be more than enough for just the one 6870 as it's not a very power hungry card (http://www.legitreviews.com/article/1605/15/) but once I decided to overclock the card a little (haven't OC'd the CPU yet), I had some interesting results in 3D Mark 11. As expected, my graphics scores went up significantly at a very modest OC from stock 900 Mhz core/1050 Mhz memory to 950/1100. Haven't touched the voltage. However, my physics scores also went down significantly, in the realm of -10%. Since the physics tests are mostly CPU dependent, the only explanation I can think of is that my PSU is already close to maxed out, so when I overclock the video card not enough power is delivered to the CPU.
Any thoughts? It's a decent, if on the budget side of the spectrum, power supply from a good company, and 500W should be more than enough to leave some room for some light overclocking.