There is really no single answer to the question of optimal temperature for stony coral growth, which is why most recommendations are in the lower end of the summer temperature averages from most common tropical and subtropical reefs - allows enough room for equipment and other issues.
Stony corals will bleach equally at low and high temperatures. The low range tolerated is around 64F and the high is around 84 although some will survive temps in the 100s for short periods of times. In certain regions corals regularly thrive in higher temps than 84 during summer without obvious issues.
Using photosynthesis to respiration ratio as a growth proxy, repeated studies have found that increasing temperatures by ~2-4F above the summer averages of the region of origin will severely decrease the ratio and often lead to bleaching. There is a high correlation to carbon fixation as well. Reproduction rates (not as much of a concern for most of us) will drop tenfold at about 2F increase from the summer average.
In lab settings scientists have a good understanding of where their test subjects come from and can thus adjust the temperature to what is considered to result in peak growth. In general that means adjusting the temp near the summer average for the region.
In our tanks very few would know the actual origin of the mother colony that and even then we’d end up with a pretty wide range. Possibly as low as 75 and into the 90s.
To illustrate, a coral from more temperate zones of Polynesia may thrive/peak near the summer average of ~77 and have a bleaching threshold of ~80. The same coral in the Caribbean may thrive/peak at 84F and bleach at 86.
