QRTRHRS (and others):
I tow a 26k equipment van behind an F450 tractor (we use all pintle hitches on our CTD 2500's). Brakes are a really big issue, especially in the mountains. Axles are right behind.
The first venture with this trailer had 3 x 7k Dexter tor-flex with electric 13" drums. Axles ran about 18k most of the time. Tire wear was catastrophic. One side is a few hundred heavier than the other, and it showed in a hurry. G159s in load range "G" don't come cheap, and I had the market cornered! Torflex axles may be RATED for some number, but they are not useable at that weight because the rubber bushings deflect enough to give the tire really bad camber (and a bit of toe). Went to 8k Dexters, pout in a lighter genset dropping axles into the 16k range (5,500 each) and now tire wear and life is "normal". For those who are limited by wheel stud hole size, you can get a "7,200#" torflex that has stiffer bushings in the same hardware as a 7k.
Electric drum brakes are another thing. They may be fine for meeting the legal requirements, but they don't even come close to slowing down the load!! When I went up to the 8K axles, I added a Master actuator and Kodiak discs and, now, the damn thing stops like no other commercial vehicle I have ever driven. Adjustment is also eliminated (a big deal in mountain towing). There have been a few maintenance issues in getting to know the Kodiak/Master setup, but things are pretty stable and predictable now. BTW, I do coast-to-coast emergency service calls with this thing.
Hope that helps light the way for those who are going to do very heavy hauling with these light/medium type of trucks. It can be done (even legally), but you want to be VERY conservative on believing the equiment manufacturer's ratings.
Pat