Have have you turned down the the hyper transport bus? Probably not a power problem, unless you psu is having it's issues. It should have enough power, as my system, similar to your with sli 7800gtx's oced, and the 165 @ 3ghz would draw 330w from the wall under load.
I think you are missing a setting or two. Loosen up the ram timing, turn the ram down, lower the HTT bus.... etc.
wes