My one tank hit 82 for part of one day this summer and was 80+ another day. Usually it runs right at 78. Ironically, it was on a somewhat cooler day when the AC was not on as much. That tank is right by an AC vent. I think I'm going to have to close that vent entirely during heating season.
Everything came through just fine. I did take action when this occurred on both days, turning off lights, etc.
There are some critters that definitely prefer lower temps and quite a few things hate wide fast fluctuations.