Cummins,
Some of the things you are asking about, i.e. load to a grawr, and stay below a gvwr, may or may not work! An Astro can I had, with both axle limits of 3100 total 6200, but GM limited gvwr to 6100, I can load to RA limit and stay under gvwr no issues.
On the 05 dually I had, and some SW 25 and 35 series trucks. The difference between the sum of the axles and gvwr is such, with out removing weight from front, by loading gear etc behind the rear. You can't get to RA limit, with out going over the gvwr limit.
Hence why some of us, us the sum of axles as our max loading vs manufactures. OR, we say screw the manufactures warranty/weight limits, and go by our states paid for limits, which are based on Federal Bridge Law limits per axle.
Reality on latter, is the 450 vs 350, will net the same max gvw of around 30k-32k before getting an over weight ticket. 20,000 on rear, 10-12,000 on front. With the F450 probably being the lower due to the 225-70-19.5 tire width. Vs an F350 having 235 or 245 width tires iirc. If the have same tire width, both will have a max that is equal.
Reality which is better, the 450! Licence accordingly. I'd do a minimum 16000 licence, drive down the road with no question on legality of it. Just as I go down the road at upwards of 26,000 with my IHC with a gvwr of 18200. 14000 with my 05 gm dually with an 11200 gvwr. 12000 with my 96 SW K3500 with a 9200 gvwr.
Too many ways to play the numbers game.
Marty