Really, you don't need a DRW for a Lance 650 and a 2-horse trailer. I know about planning for the future and all, and a 2500 would limit you as far as getting a lavish massive TC in the future, but do you really forsee that?
3500 SRW's are hard to find in certain areas. Such as Western NY state. West of Syracuse there is ONE dealer with a Chevy 3500 SRW new on the lot, and it's a crew cab 2WD. Used ones are even harder to find because they're usually clapped out F350 work trucks.
A 2500 will work fine for your purposes and leave you some room for growth.