Average temp is of no particular value. I have seen some people who claim they run at ambient temp + some constant value, which is nice, but also of no particular value. What matters is the instantainious temperature at any particular point in time. As the temp of the fluid goes up, its lifetime goes down. I've seen charts, and at the high end, being at that temperature for 5 minutes is all the transmission can stand before the fluid has to be replaced (or risk damage).