steve671,
as you can see many different opinion,
mine, it depend...
in my experience, if you keep your tank at 78-80 and one day you hit 84, things in the tank can bleach, ect
but if you keep your tank at 82-83, then if one day hit 84, things will be ok
in other words, stability is the key, not so much 77 or 81, ect...based on eric borneman, the highest is 86, while the lowest is 77, and the average is 82
so if you keep your tank around 82 you will be fine,
sam