Crazy-high NB Frequency: How do I lower it?

[oseewhat]

I'm finally getting around to overclocking my i3-530. I got to 4GHz, but after about a minute and a half of encoding a video, my computer restarted. I then opened up CPU-Z and noticed a big discrepancy between what the NB Frequency was at stock (2133.4MHz) and what it is after OCing (3056.1MHz). Given that seemingly everyone is able to OC this CPU to 4GHz and beyond (4.4GHz) I'm wondering if this has anything to do with the instability I'm experiencing.

Unfortunately though, I couldn't seem to find any settings related to NB Frequency in my Gigabyte GA-H55-USB3's BIOS. Is this because it's a fixed frequency based on other settings like multiplier, base clock, etc. - and if so, what are those settings - or is it just because my BIOS is lame?

Stock 2.93GHz:

Bus speed / BCLK: 133MHz
Multiplier: x22
QPI Link: 2933MHz
Core Voltage: 1.168v

DRAM Freq: 666.7MHz
FSB : DRAM 4:20
NB Frequency: 2133.4MHz

OC'd to 4GHz:

Bus speed / BCLK: 191MHz
Multiplier: x21
QPI Link: ~2600MHz
Core Voltage: 1.3v

DRAM Freq: 573MHz
FSB : DRAM 4:12
NB Frequency: 3056.1MHz

DRAM frequency was left at 1.5v, as were the memory timings, though I did notice that the voltage readings dropped from about 1.568v to about 1.538v after the OC.

Any assistance/insight would be appreciated, thanks!