My 7800GT runs games like DOOM 3, Halflife-2 and BattleField-2 without issue... Almost perfect infact. Instead my issue comes from running a few of the older titles that are still considered Direct X 9 compatible. While playing these games, I've had cronic issues with the video becoming unstable and stuttering after 10-30 minutes of play.
-Neverwinter Nights & Expansion packs. (Stutters after 10 minutes, and gets worse the more I play, changing the graphics settings in game does nothing to stop this)
-Jediknights: Knights of the old Republic. (Looks and plays like molassis from the get go)
-Battle Field 1942. (Seams to run "ok", but then my system randomly restarts)
-Athalon Dual Core 4400.
-EVGA Geforce 7800 GT SLI (256MB), one card only.
-ASUS A8N-SLI Mother Board.
-Sound Blaster Live 24 bit.
-2 Gigs of Kingston SDRAM.
-Twin Raptor Serial ATA Harddrives (RAID 0).
-450 Watt Coolermaster PSU.
Please note, that all system drivers, MB bios, game patches, and windows updates are current. (Right from the MFR's websites) I've run HD-tune, and Memtest86 without seeing any errors what so ever. Changing the "Video Hardware Acceleration" and "Write Combining" does nothing. The only small thing I've seen askue is the fact that I am getting crappy performance numbers from 3DMark06, and considering the potential of a system like this, I'm very concerned. Almost feels like it's a video memory leak cause by the system drivers.
P.S. Tweeking the bios settings hasn't yelded any results either, and in Taskmanager my "System Idle Process" is at 49-50% while the game is at 49-50%. I know this isn't normal.
I am running 83.40 right now and it seems to be very stable. I haven't had any problems. I can run BF2, HL2, and Quake 4 maxed out with no problems. With your system it should eat those games alive. You may have something running in the background. I would also call tech support for your card and see if they can pin point the problem.