Old overclock question.. Gigabyte DS3 w/ q9550

Maybe someone can clue me in here, I've tried to overclock my Q9550 from stock speeds via bios (not that Easy Tune stuff), and very often I can adjust the speeds however it seems to work only once, i.e. change from 333 to 350 or hell even a tiny 340 adjustment! It'll reboot just fine, I can play on it all day or whatever at the new speeds, then shut down, and the next time I boot (or try) it just will not get to post. Turn off and on a few times resets it back to the stock settings, just wondering if this is a known issue with the p965-ds3 (rev3.3) board, I have the latest firmware to support the Q9550 chip, and while yeah I could upgrade, there's still a good amount of life left in this chip.