I dont know what type of cooling you have but 1.35v- 1.4v for CPUNB can help stabilize things when running Higher NB..

Also if your Mobo has a CPUNB to SB voltage setting (this is for the comunication from CPUNB to SBchipset/Memory)
You can run this around 1.3v-1.325v with stock NB/SBchipset cooler.This helps keep the Ram stable and allows Higher Ram freqency and Tighter timing as well..

little things count with Phenom for Stable clocks. NB @2400mhz is good all around freqency..2600mhz and higher require real good cooling especially above 3.3ghz..You can usually clock Higher CPU with Less overall NBfreqency above stock paramiters..

Ive found,,
Stock CPUnbvolts = 1.3v up to 3.2ghz and say 2400mhz.

3.2/2000-2500 with 1.35vCPUnb
3.3/2000-2500 with 1.36vCPUnb
3.4/2000-2600 with 1.36v-1.4vCPUnb
3.5/2650-2700 with 1.55vCPUnb(max volts) My max stable.

By looking above ,, 2450mhz at any given CPU freqency with minamal xtra volts is ideal..

Of coarse this was with SB600 The Volts will be about the Same with 9950/SB750 for CPUNB..The CPU is main factor for NBvolts..Now a 750chipset( CPUnb to SBchipset) will be a little lower because the SB750 does a better job.

Hope that made sense..
Your Cooling will determin the overall Oc.
I just Try to find Max CPU clock @2200nb before raising the CPUNBvolts.. More CPUnbvolts will allow the CPU to Clock higher...Raise the CPUnb and Scale the Volts in Slow increments to find its max. Then Turn the NB back down to say 2200mhz with the Higher Volt setting.

Next try rasing the CPU clock Higher while keeping the CPUnb @2200mhz. You probally will be able to hit 3.4ghz no prob. For me to achieve 3.5ghz i have to run CPUNBvid @1.45v+ and above 2200mhz NB or 3.5ghz wont work. Each chip is differant. Ive found the Higher the Phenom goes the Nb seems best when raised a little above stock ,,Goes in hand with the extra CPU clocks//CPU performance.