I borrowed a 7950 GTO 512Mb from a friend. Replacing my 8800GTX with this has stabilised my system. No sign of crashes at all, been playing in Source engine for about 4 hours now.
The 7950GTO only requires one power connector, unlike the 8800TGX which takes two.
So, either I have a bad graphics card or the power supply is not stable enough to supply on both 12V PCIE connectors. I suspect it is the power supply. I asked my friend to run CPU-Z on his gaming rig and send me the output file.
His voltages:
Voltage sensor 0 1.33 Volts [0x53] (CPU VCORE)
Voltage sensor 1 1.20 Volts [0x4B] (VIN1)
Voltage sensor 2 3.26 Volts [0xCC] (+3.3V)
Voltage sensor 3 4.89 Volts [0xB6] (+5V)
Voltage sensor 4 11.84 Volts [0xB9] (+12V)
Voltage sensor 5 -6.02 Volts [0x5E] (-12V)
Voltage sensor 6 -10.56 Volts [0xA5] (-5V)
Voltage sensor 7 4.95 Volts [0xB8] (+5V VCCH)
Voltage sensor 8 3.10 Volts [0xC2] (VBAT)
Temperature sensor 0 36°C (96°F) [0x24] (TMPIN0)
Temperature sensor 1 40°C (103°F) [0x28] (TMPIN1)
Temperature sensor 2 46°C (114°F) [0x2E] (TMPIN2)
Fan sensor 0 975 RPM [0xAD] (FANIN0)
Fan sensor 2 3590 RPM [0x2F] (FANIN2)
My voltages:
Voltage sensor 0 1.17 Volts [0x49] (CPU VCORE)
Voltage sensor 1 1.84 Volts [0x73] (VIN1)
Voltage sensor 2 3.34 Volts [0xD1] (+3.3V)
Voltage sensor 3 4.92 Volts [0xB7] (+5V)
Voltage sensor 4 0.51 Volts [0x8] (+12V)
Voltage sensor 6 -3.33 Volts [0x34] (-5V)
Voltage sensor 7 5.08 Volts [0xBD] (+5V VCCH)
Voltage sensor 8 3.26 Volts [0xCC] (VBAT)
Temperature sensor 0 39°C (102°F) [0x27] (TMPIN0)
Temperature sensor 1 23°C (73°F) [0x17] (TMPIN1)
Fan sensor 0 1112 RPM [0x25F] (FANIN0)
As you can see, his +12V is operating at very close to 12V, whereas mine is not. Can anyone confirm if that means my PSU is defective?