Running with more than 7 creates more problems than it solves. Hash rate does not improve by much as GPUs are at 99% already, so what is the point. To crash cgminer?
GPU being at 99% has nothing to do with how much of that is USEFUL WORK (i.e. shares)
I have a windows workstation w/ 3x 5970 water cooled which has been running for 7 months now.
If you are driving a display it is a good idea to set that GPU (AND ONLY THAT GPU) to d intensity. Too high of intensity on the GPU used by the OS for driving the display can cause system instabilities. I set 1 core to d and the rest to 9 and the rig runs fast and efficient without crashes. This is heavily overclocked and overvolted. Lowering the intensity of all GPUs even those never used for anything other than mining is simply wasteful.
5 threads per GPU? What exactly do you think that accomplishes?