The F-350 SRW should have about 7,000 GVW at the curb, so the truck should carry about 4,400 pounds if you have the GVWR correct. It might be 11,500 pounds? Are you looking at another 4x4? That is a 400 pound option, and will take away some of your capacity.
The old truck might be more value with the airbags. The 865 pound cargo rating of a F-250 diesel 4X4 crewcab is why in 2000 I told my brother - a engineer at Ford to stop putting the diesel in the F-250's. However with nearly 60% of their Super Duty trucks sold with the PSD, they started making the GVWR higher, a wise decision that has helped every truck owner since!
Good luck with your newer truck! Make sure that it already has a coolant filter, or install one right away. Napa #FIL 4070 is the filter, and kit # FIL4019 is the kit to install it on the heater hose of any vehicle. It will filter out the junk from the coolant, and that will keep the radiator and oil cooler clean. .
Fred.