OverclockingWe used ATITool to search for the maximum core and memory clocks but the results were much too high. We then manually dropped the clocks until we were left with a completely stable system that could complete our testing suite without visual errors or crashes.
The final overclocks of our card are 674 MHz Core (6 % overclock) and 736 MHz Memory (5 % overclock). The overclocks are most probably limited by the cooling solution, but consider this card is designed to be silent not to be an overclocking monster, so the limited overclocking should not be a major concern.
With the 8600 GT ZONE running completely passive, without any case fans the temperature rises fast and reaches really high levels under load. The NVIDIA thermal protection ensures that the card does not get much hotter, but it will cause hangs in rendering that continue once the temperature has dropped again. Zotac recommends having at least one case fan that gets the hot air outside of the case.
Once we put a slow running 120mm fan in the front of the case the temperature dropped to perfectly safe levels, even with overclocking the temperatures did not rise much more. Such a case fan in the front or in the back is common in most cases today.