The only point where it would be important to overclocking is if you were overclocking to the point that power delivery to the CPU was adversely affecting power delivery to the PCH. If this is the case, you need to get a better power supply. I can't think of a case where I've ever had to fiddle with the PCH settings, much less its voltage.
Keep in mind that the PCH only handle's IO tasks according to industry standards. Nothing on it can be overclocked.
Yeah you should. If you're looking to build a new system though I'd go with Asus or MSI over Gigabyte any day.
Gigabyte is a decent OEM, as are EVGA and ASRock but they're not the best. Those motherboards will overclock well for a bit but over time they will lose their punch and you'll find yourself suffering BSODs and having to fiddle with voltages just to get it stable again.
Enthusiast boards from Asus and MSI will continue to run merrily along long after a Gigabyte board has bit the dust.