Try adjusting the voltages with MSI Afterburner beta version. I was able to drop the voltage from 1200 to 800 on each core with my 7990.
unfortunately this isnt working for me .. i have a 64bit system.. and the beta is only available for 32bit systems ... and besides the gigabyte cards are locked... with the normal afterburner version i cant change the value for the corevoltage
No idea what you're talking about...i have a 64 bit system and am using the MSI afterburner beta just fine. Gigabyte cards are notorious for their voltage locking. But I'm not sure if they're actually locked on the 7990s.