"With most Ford based specs sheets I've looked at, to carry the full GVWR "legally", all 4 corners have to be loaded to exactly the capacity of the tires. "
I sincerely doubt that statement. I run my E-350, GVWR of 11,500# at or at least very near that max number on almost every trip. My tires are nowhere near their max load capacity which would necessitate running all 6 at 80 psi. If you do you will have the worst handling Class C ever.
Heavily loaded I run the fronts at 65 and the rears at 70-75 and that still leaves a serious fudge factor before getting anywhere near their max capacity. My FAWR is 3,800 and the Michelins are rated for 5,340# {2,670 each}. The RAWR is 7,800 and again the Michelins are rated for 10,680.
Running these pressure my rig drives and rides great. Big rigs do not push me around and wind up to 35 mph is still two finger steering. I'm sure the heavy duty Bilstein's help a lot but it would be hard for me to imagine a better handling motorbhome than mine.... this after 50,000+ miles over the last 6 years.
:C