Generaly you would lower the multiplier of the CPU to keep other frequencies from rising up and limiting the CPU overclock.
You have it backwards.
The Black Editions have unlocked multipliers. For those, you do the "increase multiplier, test, increase voltage" cycle until it doesn't work. Then you back it down until it does work.
Then you work with frequencies and do the same thing until you either reach your goal or cannot go farther.