I'm personally of the opinion that keeping them at sustained high temps is actually not at all good for them. But then my observations (like others here) are anecdotal. In my experience Platyrhincus do benefit from a temperate schedule of warm in summer then cool in winter. I do not feel sustained high temps are good for these fish.
They are not coldwater fish but they ain't tropical either they do seem to do best with a seasonal fluctuation. All North American gars seem to share this trait, especially Osseus, Spatula and Platostomus. (I assume Oculatus does as well but until recently I have not had a chance to work directly with them as far as Captive husbandry is concerned.)
Any how take it for what it is worth.....