SATA and Overclocking

I’m looking at an opportunity to mess with overclocking with an older motherboard (ASUS P4B266) which seems to have some primitive OC features. I’ll be installing SATA drive(s) with a PCI SATA I card. Google suggests that SATA on-board controllers do not work very well in an overclocked system. But will an add-on card suffer from the same problem? Is that why a PCI lock is used?