From my understanding, it's debatable on either side - high or low, but stability being key. Higher temps are closer to the natural conditions found thus would be ideal for growth BUT in a poorly maintained system, it could be problematic.
At higher temps, salt water loses some ability to absorb dissolved O2
added to that, fish and coral metabolic rates increase, creating more waste & using the dissolved O2
Higher temps result in faster growth but also higher impact of bio load and O2
use. It's a trade off either way, but stability probably has more impact long term.