I heard here, the 2500's have heaver springs in the back then the 3500 SRW. Thus the 3500 SRW has a better ride. The reason they can do this is because the 3500 SRW has the overload springs which take the load once they come into contact.
Mine also has something that is important to me, "this piece of paper that says it can haul a slide in camper".
The 3500 SRW is rated for a couple more hundred pounds bed weight.
The 3500 SRW with the 6 speed is rated with a GCVW of 23,000 lbs, not sure what the 2500 is.
Plus for that extra money, you don't have to add air bags, extra springs or anything else. Some people elect to add these rubber blocks (forget who sells them) that decrease the space between the helper springs and perches, this stops the truck from dropping so far before the helper springs start to work.
How well does it work? Don't know yet, hoping to take the 5er out in 2 weeks. The pickup camper don't get used until around July.