A little more research on Ford's spec sheet and I got some more numbers for specs. 
Rear wheels: 3590 each
Tires: 3640 each
Rear springs: 7000
Rear axle: 7280 (Ford Sterling)
So I see where the 7000 lbs rating is based on that spring pack rating, however the axle rating on the Ford Sterling doesn't seem that much higher. Does that seem right, or is the Ford Sterling much higher? Again, I'm more concerned about the manufacturers capacity for components, as in I have no problem upgrading tires and wheels and adding airbags or more leaves to the springs, but I want to make sure I'm not exceeding the axle rating as I have no way to upgrade that other than a new axle. And for all that cost, yes a DRW makes more sense. 
I prefer a SRW truck for the big reasons, parking, 4 tires vice 6... etc. However if the modification cost for the SRW truck is the same or more of the premium for a DRW truck, then getting the DRW makes more sense. I'm just trying to understand what I'm looking at.
...of course I could also just go Lance 815 and fit the whole thing in the long bed without needing an extension for towing...