The HD4870X2 did run a bit warm....as did the HD4850 with the reference single slot cooler (mine idled at 80-85C and would reach 105-110C under load). Typically, once the stock/reference cooler was replaced with a proper (aftermarket) cooler, the temps would become reasonable (assuming the cooler was installed properly).
@OP, what case do you have? where are the fans located? how are the fans configured?