Gigabyte GA-M68MT-S2P am3 mobo?

Well first of all the motherboard is the heart of your PC so don't skimp out on it. Second of all, yes it should handle an overclock fine I know people with the board and they can get above 4ghz with their phenom ii x4 955. Third of all, it's not the motherboard that determines whether the 4th core will unlock for that cpu, it's the cpu itself. In the CPU manufacturing business there is something called binning, basically the end result is not all CPUs are created equal. You may get one that unlocks no problem, you may get one that doesn't at all no matter what you try. I would just get an X4 and not leave it up to luck on whether or not it'll unlock or not because there are always when it won't. Doesn't hurt to try th ough.