Historically the difference between a 3/4 and 1 ton (SRW version) is a bigger spring pack for the 1 ton. Nothing else is different.
Some of the newer trucks (Dodge in particular) use different spring designs.
When you move up to a dually, it's a whole different rear axle.
For a 5th wheel, it's all about the pin weight (yes, check all the stats) and each move up will get you more capability to carry pin weight.
Moving up to a 1ton SRW is negligible cost and negligible impact on ride quality empty, so unless there is a big registration fee jump, go for the 1 ton.