Raja, I asked asus tech support:
Quote Originally Posted by Zoson
[Problem Description]
Is there any way to directly or indirectly control the voltage of QPI PLL on the Rampage 3
Extreme?
And got this reply:

Dear Valued Customer,

Thank you for contacting ASUS Customer Service.

My name is Stacey and it's my pleasure to help you with your problem.

Please enter BIOS>Extreme Tweaker>CPU PLL Voltage to adjust it.
You could contact with me if you have any other questions.