theres two different voltage. nb and cpu-nb. cpu-nb is the memory controller while the other nb controls your pci express lane and memory and others. what he has to do is set the cpu-nb if he wants to get a higher frequency. dont get those two mixed up.
I cannot find one specifically for the NorthBridge other than the CPU-NB.
The Board has a max of 4Ghz NB Freq. but it doesn't have a voltage adujustment?