The weather here is pretty consistent, and rarely changes quickly.
If the peak temps during the day are 80 or higher, I'll go with at least 89. When I had my ITC installed (pre-stolen, I guess) I went 89 in cool weather, 92 (NOW 91) When it was hot.
Now, I'll go 87 most of the time, and 89 if it's in the 80s or higher.