pll voltage has absolutely nothing to do with vcc voltage. its the voltage that the internal phase locked loop needs to lock all the cpu phases to the analog pll clock generators supplied reference frequency and fsb phases. you only need a higher pll voltage when you can see through say cpu-z or bios info that your fsb frequency is bouncing either side back and forth from the target frequency, since deviations in the fsb frequency as usually a result of the cpu phases in misalignment to the fsb phases with respect to an insufficient input voltage on the internal cpu pll.