The temperature under heavy game stress for the R6790 load stabilized at roughly 65 Degrees C only.
The generic rule under load is that everything under 65 Degrees C would be fantastic. In-between 65 and 85 degrees is a normal temperature. Anything passing 85 Degrees C we simply feel is over the top.
Obviously your PC has an effect on load temperature, please make sure your PC is well ventilated at all times, this will help you improve the overall GPU temperatures.