I got a new HIS HD4870 , but this thing runs VERY hot (70°C ) , but after gaming it hardly goes up (i think the fan speeds up to maintain the temp ). On my old HD 3870 i have a Zalman GV1000 Cooler , would it be worth fitting this to the HD 4870 ??? Or should i just AS5 the stock cooler and speed up the fan ????