The biggie is the pin weight, but to me the overall length is very important. I have driven in some windy weather with a 3/4 ton 98 RAM and a 32.5' 5er and I know what it's like to be pushed around by wind and it can only get worse with length. I also know what it's like to tow in wind with a Dually and 37.5' 5er, it was rock solid. I know different situations but the fact is the longer the rig is the more it will effect the TV.
A relative just bought a 42' Bighorn with a GVWR of 16K, he has towed it with his 03 RAM short bed 2500 and he said the RV overpowered the Truck. He is looking for a new truck and I recommended a 3500 DRW. He does not like the idea of dealing with the dually so who knows he may end up with a 3500 SRW. The length and pin may be fine for his rig but the length pushed me to recommend a DRW.