NB Frequency...??

What does this NB Frequency mean? Thanks..

The NB on Intel is the cache operating speed. That's what it's listed under in the BIOS. It can offer up a bit of added performance if raised manually but can also require you to add a bit more core voltage for stability.

I will only add that on Z chipsets (115x/1200 sockets) it's not giving much so it's not worth playing with (at least out of competitive benchmarking). Depends on the chipset, the cache voltage can be tied with CPU voltage so it can raise CPU's temperature. On X Intel chipsets or on AMD, it helps in higher memory bandwidth as it's also a memory controller clock.