I am also having a similar problem. - However what I did is I recently installed a watercooling system (Aquagate Duo Viva) to my 8800GT 512MB. I put all the RAM sinks on, and on the voltage regulators etc... Temps from idle went from stock 67 degrees to 45 degrees idle, so temps were way better. However one RAM sink came a bit loose, and my games were freezing / crashing with a Send/Don't send MS message (COD4). I then got a bit fed up, and put the stock cooler back on, and applied new thermal paste to the GPU, and my temps were a bit better than the stock used to be. I am still having the crashing problem. Anyone think that re-using the thermal pads from stock cooler could affect memory temps? I will watch this topic.
Is there anyway it could be our northbridge temps causing this? I felt the NB heatsink and it is really hot (Summer here in South Africa)