Well, the on board sound and NIC are still technically PCI devices, so OCing would likely affect them. I never tried the OC BIOS when I had a ECS K75SA, so I can't really discuss that board specifically, but I have noticed a few situations where on board solutions handle OCing better than real PCI cards (I dunno, maybe because the noise associated with the connectors and longer trace lengths???). However, the only real way to tell is just by trying it out.