Ok, I can't speak to the 19.5's or the longer tire life yet but, my SRW CargoMax starts life as a 12,300 lb gvw DRW Chevrolet Cut-away..CargoMax then change the DRW that are 16 in over to a SRW 17.5 rickson setup..then re-certify the chassis to 10,000 gvw...they can do that by moving to the 17.5 wheel and tire which as a 12 ply range at 3750 lb verse the factory 16 in. 6 ply rated at 2680....now GM use the 16's as a dual setup on the rear to get to the 12 ,300 gvw but if left as the tire on the srw, the load capacity wouldn't be there...
So yea the increase in load capacity is certainly there and while the rear tires make alot of noise (they are a M&S) they seem to be wearing good...