Just purchased some new larger tires so I am considering improving braking ability. Did you also do the front? I would not expect any improvement with just doing the rear since the front do most of the work.
Using different compound pads is an easy way to play with brake bias. Although the fronts, ultimately, are capable of greater braking force due to forward weight transfer(braking/downhill/etc.) using a more aggressive pad in the rear, does still increase overall braking performance up to the point rear traction is exceeded. Increasing rear brake bias/and or performance, is often desirable while towing. Race vehicles, and rally cars in particular, often have adjustable brake bias to aid in rotating the car, or decreasing brake induced understeer.
In general, mo' braking, is a good thing. If I towed, I would have considered slotted rotors; under hard use, the slots help to prevent pad float, as they allow pad gasses to "escape" from the contact surface. Modern compounds are very stable, but with a trailer, in a panic stop, you may encounter it.
For pure offroad use, I would prioritize modulation over ultimate stopping power. With good modulation, creeping over/off of, say, a sand covered rock, is doable. A stronger pad, with less "feel" would make that more difficult. ABS can be problematic in scenarios such as this, imo.