Overclocking with nvidia display utility--reverts to original speeds after restart?

[hynat]

It seems that whenever I overclock my BFG 7800 GT OC (a mere 50 MHz, 425 to 475), check "apply these settings at startup", press apply, and restart, it reverts back to 425 MHz. Is this because the driver thinks 475 MHz is not "optimal"? The optimal speeds that it detects is actually 500/1.15 GHz, which shows too many artifacts. but at 475 there are no artifacts.

How can I make it keep the speed?

Thanks..