o/cd opteron prob.

i have a gigabyte k8n sli motherboard that seems to be behaving odd. i can
get it to run at 290 FSB with an Opty 144, this gives me 2.6GHz but in order
to get more i tried the overclocking software that came with the board.
alas it does show the board running at 300 and 310+ MHz FSB but the overall
speed doesnt increase above 2.615GHz. Cpuz reports everything stuck at 290
FSB??
Last night i dropped the CPU Voltage to 1.7GHz instead of 1.75 and suddenly
it rebooted at 2.7GHz and even Cpuz showed everything at this speed with a
300MHz. But i had to sleep and when i tried to boot this morning guess
what? yes it was back to 2.6GHz even using the settings left from last
night. even when it booted at 300 cpuz said 290. Why is this 300 in BIOS
but 290 in cpuz and in control panel?
why is the lower voltage required to get a better FSB.
TIA

Robin