86 is the temp where the immune system functions the best and anything 82+ will keep ich from growing in tank as well. Obviously in outside conditions they have to be able to stand more than 72 degrees so it's strange people worry so much about high temps. The only drawback is they will kick up their metabolism and have much more appetite which can lead to more waste.
Optimal temp for optimal bodily functions are not same for all living organisms. Wouldnt raise temp in treatment of fin rot although 86F are manageable.
Ich at 82+ will speed up their life cycle and will proliferate in presence of hosts.