I have my eVGA 7900GT Manual Overclocked via the Display settings to 558MHz core clock frequency and 872 MHz memory clock frequency. It idles at around 53-54C, and after running 10min or so of RTHDRIBL it's hitting 74-75C. Would it be a good idea to get some kind of after-market cooler? What type is best for a 7900GT? I see people mention Zalman as a good name.