There is a lot of variation from one person's set-up to another on how much vcore they're going to need to be stable.

On the Mainboard tab of CPU-Z it shows what chip is being used to report voltages. My Asus P5B uses a Winbond W83627DHG which CPU-Z is programmed to read correctly.

Use a DMM to confirm but until then go by CPU-Z. The programmer put a lot of effort into supporting as many boards as possible, including yours, to correctly report core voltage.