Even with extreme overvolting, overclocking and pushing the power limit to +50%, the GPU temperatures never go above 60 degrees Celsius. With watercooling, maximum power draw becomes the biggest restriction - you can't push unlimited watts through your components, even if they are running cool. At X volts or Y watts, they will start to produce errors and/or degrade quickly. I am preparing new articles about that and about other aspects of serious BOINC/Gridcoin GPU mining, stay tuned.