It's not what you can tow, it's what you can carry as in payload. Especially with 5th wheels as pin weight will add up quicker than fast as storage is 75 percent of the time forward of the axle. Personally with a 250/2500 series it's usually around 12k and under with say 10k being optimal IMO. With a 350/3500 series in SRW add 2-3k to that with 12-13k being optimal. More than 15k and your in dually territory. Now some will dispute these numbers and tell you different and that's ok. As I said, it's my opinion and optimal numbers with my experience. I have a Grand Design 303RLS that is around 11k loaded and have a 3500. I'm a very, very firm believer in overkill when it comes to myself and my family's safety. And others on the road deserve for me to be safe also. YMMV.