A very interesting topic. Here is a good study of Trout in Southern California. One point brought up is the variation is what optimal conditions are for trout in other parts of the country (Pacific NW v. So Cal). My guess is that trout here in the Southern Appalachians are closer to So Cal trout than Oregon)
The top end of good growth
was almost 72 (22C)! and that growth dropped off at 77 (25C).
Maybe we are overly concerned about temperatures. I think the most worrisome aspect of our weather is the drought. I think that has much more to do with stress than water temp.