You better get your info from ford from here on out, there is no difference in tires between 250 and 350srw.
The f350 has an overload spring which can be ordered on the 250, the 350 has hydro boost brakes and 250 has vacuum. Also the 350 does have a slightly larger dia rear axle shaft with higher spline count.
All this info is right one fords website.
YEs as for me I am running airbags, my truck is level but i do know i am over my GVWR when towing the new trailer. Am i sweating about it no, i just know my future will have a 350drw in it.