One thing I noticed swapping from rims to discs touring was that I needed a big front disc to get rid of heat. But I'm probably a bit of an outlier touring wise. I travel heavy and like descending like a loony. Fast into corners and heavy braking. I turned my 180mm disc blue and burnt the paint off my pads. Up to 203mm now. I ended up with discs because I scored some disc wheels with a Rohloff