CPU/NB is the NB in the CPU. basically the memory controller. Since Phenom IIs memory controller is 1333MHz if you set your ram higher that that you may need to up the voltage a little since you are overclocking the memory controller.
The NB is just the normal one on the board and you shouldn't need to mess with it.
You have a black edition though, ignore the memory.speed, leave it at 1333 and just use the multiplier to eliminate complexity. once you find the Max clock u can go back to memory. push the multiplier up, add voltage till its stable or you hit the safe limit and watch your temps