I would really try to get all the brake specs....size of caliper, number of pistons & xsectional clamping area, diameter of the rotors etc. My comparison would be poor, since I went from a 97 that was right near the end of the drum brakes and notoriously bad rear brakes on GMC, to a 4500 with unbelievably huge disks all the way around. I weigh around 19,000 pounds, and I can stop faster than I could with my old 97 weighing about 9300 or so. I've had to do panic stops on both. Night and day better brakes, even over the actual weight difference. Hell, they are a lot bigger than the F550's too.
I firmly believe that brakes are the unsung heroes of the camper carrying truck.....I'd work hard at tracking down the brake specs for the two models you are considering. (and then I'd STILL want to get the 2500...... :) )