I'd venture a guess that you are doing something wrong -
Is your BIOS up to date? Are you using AOD, the BIOS or the 'Auto-Clock'?
What is your reported CPU and NB voltages? We need information on your RAMs.
At stock volts 3.4GHz and 2200MHz IMC/NB should be a 'slam dunk' at 200x17x11 unless something wacky is going on. Disable spread spectrum and ungang the memory controllers. Disable C&Q.
How did you get to 3.33GHz? Is this a combination of CPU multiplier and AMD base clock? Did you just raise the base clock like 222x15? If so it's possible you increased you ram speed by 11%, too, which may be casusing you problems.
The default/stock voltage on the PhII 940 is 1.35V. You probably won't be able to get a good NB clock while undervolting.
I must raise the NB-VID voltage to something like 2.25V to get the NB to 2.4Ghz stable and 2.6Ghz benchmarkable. (I can't tell you the exact voltage right now... I'm on the road. When overclocking the NB/HT I ALWAYS set both the NB and HT manually; the HT must always be lower than the NB, and I generally leave the HT at 1.8GHz. Trying to raise both can cause instability and it has been shown that a faster HT doesn't really give you any performance gain, you get the gain with the NB increase.
PLUS: When increasing the NB I had found on an older BIOS that the PCIe clock speed goes up also... so I generally set it manually to 201Mhz so that I don't get weird results. I haven't checked lately to see if it still goes up. When set to AUTO and overclocking the NB to 2.4GHz/2.6Ghz it was going up to like 230Mhz-250Mhz which was a bad thing. Keep an eye on it.
In my bios for that motherboard I set the following clocks:
CPU Northbridge Freq x12 (for 2400Mghz NB.)
PCIE Clock 101. (To lock it so it doesn't go up to 130Mhz.)
Then I set the following two voltages:
DDR2 Voltage +0.25V. (To go from 1.8V to 2.05V on the memory.)
CPU NB VID Control +0.250V.
NOTE: I set all my memory timings manually because I have found that it is more stable than the bios and/or memory defaults. The default is to use 127.5ns on the TRC(?) and that isn't as stable as the 195ns.
Mine are: 5-5-5-15-2T-4-195-195-195-195-6-3-31-4
My machine is stable at stock. In addition I can go to 2.6Ghz (x13) on the NB and it will work for a few hours before having problems. (But I don't like problems so I back it down to x12 or 2.4Ghz on the NB.)
If I want to overclock the CPU I have to increase the CPU voltage and multiplier. I can easily get 3.4Ghz on stock voltage but have to go to 1.4V to get up to 3.8Ghz. Anything more requires more voltage. (Generally I leave the CPU at stock clocks because I like the Cool and Quiet to work correctly and I like my machine to be almost silent. Eventually I plan on water cooling of my CPU/NB and all GPU.)