Several people run their tanks at 80 with no issues. In nature the water temp rises by 5 degrees in the summer normally as well. They can not sustain a continual rise though. Say it peaks at 82 this year, then goes down to 79 over the winter, then up to 84 next summer, then 86 the next summer. That is what is happening in the dieing natural coral reefs.
The only side effect, and one of the reasons that people run cooler tanks is that it slows the metabolism of the fish and plants. It will slow growth, but also lowers the chance of some deceases
My chiller is still available and actually was run on this exact tank. This was my old seahorse tank that he purchased.