I don't know what software your using, but AMD Overdrive is the best software from overclocking, ive seen. But if you want to do it in Bios, just bump up the Multiplier, not the Bus speed. Take advantage of that black edition. Then once youve reached a max ovreclock on stock voltage, add a little voltage to it.
I'd think the chip manufacturer wouldn't be putting out software that doesn't match up with the hardware it just produced. Wouldn't be the best business decision.
AMD Overdrive is horrible about giving the correct voltages. I have my 965 running at 4ghz with 1.45vcore in bios and software states it is 1.35vore which is wrong! The bios is the best place to overclock even though it is not as easy.