Actually the smaller rear axle diameter goes in the gas version F250 and the 250/350 srw diesel as always gets the larger rear axle diameter. The 6.7 diesel has lots more twist vs the gas = higher truck GCW numbers which are the same for the 6.7 diesel in both trucks.
Axle diameter doesn't carry weight on a full floater rear end anywayz...just the axle tubes.
The F250 with the camper package or heavy service package comes with the same front and rear suspension as the F350 srw.
Those that are looking at F350 SRW keep in mind they comes in several gvwr numbers from 10000 lbs on up to 11500 lbs and have three different rawr packages.
Gotta' agree with 4X4ord on the F350 srw. IMO the 250/2500 trucks are the most under rated LDT on the road.