Why are you using such a low intensity? 820KH/s is pretty bad for these cards. They should happily run 900 with very minimal tuning.
Temperature. Too hot where I am at the moment to go any higher.
You find intensity increases temps? I haven't observed that. The number of threads you launch shouldn't affect power consumption (and therefore heat output) unless you are talking about very low intensity. Only clocks and voltages mattered in any of my testing.