250/350 or 2500/3500 usually have the same "towing" or pulling capability. The big difference is the payload, which includes, you and your passengers, the hitch, tools, other stuff in the truck bed, fuel, and 2123+ lbs of pin weight from the EMPTY Augusta sitting on the 5th wheel hitch. That all easily adds up to over 3000 lbs before putting any gear or any water in your trailer. If you check the payload specs on 250 or 2500, you'll find that you'll likely be exceeding the truck's payload spec, which puts too much weight on the rear axle and not enough on the front axle.
The price difference between 250/350 or 2500/3500 is minimal (~$1000). On the GMC truck the payload difference is about 1000 lbs, depending on model.
On the other side of it, a lot of people no doubt are towing big rigs with 3/4 ton trucks and haven't had any apparent problems. There are some 250/2500 truck configurations that offer sufficient payload. But for $1000, you should go with the 1 Ton 350/3500 and avoid overloading.
Btw, I shopped the 2010 Dodge 3500 single rear wheel. The payload spec was almost the same as the 2500. Yes the 3500 dual rear wheel has sufficient payload, but shame on Dodge for crippling the SRW model.