Unlike many other films, I strongly recommend using box speed for TMax films. And I wish I could give a firm answer respecting TMax developer. But as far as related TMax RS is concerned, it was engineered in the first place to achieve a longer straight line clear down into the toe than common developers like D76.
But you need to understand some of the history behind that. Back then TMax was intended as the silver bullet replacing several popular older films. One of those was the usage of Super-XX for sake of RGB color separations from color transparencies. Dye transfer printing was still commercially alive, at least for awhile. An especially long consistent straight line was needed for that kind of purpose, plus relatively high contrast potential at the same time. And it was discovered that 75F was the sweet point in that respect.
But that doesn't mean that level of temperature is ideal for general photographic purposes. In fact, there is a distinct risk of edge frilling that hot. I ran plenty of very careful tests involving an expensive thermoregulator that consistently kept temp within 1/10 deg of that. I even spoke in person to one of the people involved in that 75 F specification. Somehow things got stuck in that gear after the original reason was long forgotten. But that doesn't mean you have to do things that way. Less temp, maybe less time too might be wise to experiment with. Or just go back to a more comfortable developer.
