I thought I'd share my good fortune with fellow users who may be on the lookout for cheap graphics cards with great overclocking potential. I have two XFX 9600 GT (700/1000/1750 default core/RAM/shader) on sli mode on an older board running WinXP x64 SP2. Specs:
Seasonic S12 power supply 600W
DFI LANPARTY UT nF4 SLI-DR Expert nForce4
Athlon 64 X2 4400+ Socket 939
2 gigs of matched Corsair RAM (Corsair TWINX1024-3200XL x2 - four 512 DIMMS in total)
Creative X-Fi Extreme Music
2 BenQ IDE drives (DW1650 & DW 1655 LightScribe)
1 Pioneer BDC-202 SATA BluRay reader/DVD burner
3 SATA hard drives
Latest nVIDIA ForceWare X 185.20 graphics drivers
Latest nForce v15.23 chipset drivers
I managed to get the graphics cards all the way up to 900/1030/2250 using AtiTool and without modifying any voltages. I only kept the PC case open and positioned a small desktop fan aimed at the cards. With this setup I played graphically demanding games at highest squality ettings for 3 weeks now and haven't had a single crash. Played Gothic 3 - Forsaken Gods, Dead Space, Far Cry 2, Call Of Duty 4 - Modern Warfare, Call Of Duty 4 - World At War and GTA IV for hours with resolutions of 1920x1200 and highest settings (I used the -norestriction -nomemrestrict options to get the highest settings unlocked in GTA IV), and the cards never got any hotter than 55 degrees with no crashes or strange artifacts whatsoever! What also surprised me was the Seasonic's ability to provide enough power for the graphics cards as well as all my other hardware and the thing is only 600W!
When not playing games the cards stay a cool 45 to 48 degrees. Unfortunately I couldn't get the RAM higher than 1030 without facing stability issues, but with a core of 900 working fine, I'd say I'm more than happy! Hope someone may find this info useful!