In theory the flash SHOULD make it just like a DDR, no registry hacks required, but that doesn't seem to be the case.
So essentially, flashing the bios isn't worth the risk.
HOWEVER, I do use Linux at times, so flashing is the only way I know of to get the card to run at 166 in that OS.
Sorry to hear about the memory timings. It's ok once you reboot, unless you set it to do it on reboot everytime
And a question.. you say so you don't have to do the reghacks everytime you install windows. I don't know if you know it or not, but Raid-On does all the registry entries for you