My primary driving force on the rear brakes is the discontinuing of repair parts. You are pretty limited in what can be accomplished. A bigger piston gives more surface area so more pressure on the pads. It also requires more fluid though so there is the possibility of the brake lever bottoming. A bigger rotor gives more leverage, but reduces ground clearance.
There is some hope for better braking though. Jeff in using a dual piston caliper gets a little more squeeze from the caliper over a floating caliper. This is because not only does the one piston have to move twice as far which is a wash, but it also has to slide the caliper body on the pins. The drag on the pins reduces how tight the caliper can squeeze the pads. Now in the Pilot and Odyssey rear caliper, like many brake calipers, the pads are located by the caliper body. So the system is trying to slide something which at that very moment has tremendous side load on it. The calipers I am using for the front brake kit locates the pads with the pins threaded into the bracket. The caliper itself slides on those same pins. Since it does not have the side load of the braking force on it, the calipers can slide much easier and nearly all the the fluid pressure acts to squeeze the pads together. One caliper I am considering for the rear works a similar same way.
Another thing I have thought about theoretically is two smaller calipers instead of one large one. Some of a pad is riding near the outside of the rotor with more leverage and some of the pad is riding closer to the center. If the pads are smaller, more of it is near the outside. Hence you have more leverage with the same size rotor. That may be the thinking behind some of the newer race calipers that have really long narrow pads. The pads on the calipers pictured above are about the same area as what the ones used on the Drakart were, but are longer and narrower.