Hi Shooter,
Well, I think I would ask myself a bunch questions and write down the answers. Stuff like.....Am I going to cook other things at the same time I'm smoking my favorite meat? Do I have enough room on the unit I use now? Keep in mind, the Lang cookers can work as Grills or Smokers. So if you have a grill with similar dimensions to the 48 and its not big enough....? Are you interested in the trailer units? Is storing it a problem? Are you willing to leave it out in the weather? Are you $$ paying to have the unit shipped because the price may be similar for the 60 and 48?(shipping is very expensive for these big units)
Personally, I am wicked happy with the 60 and it has truly made cooking easy for me. I can smoke 6 or 8 chickens beer can style and still have space to do beans, veggies, meatloaf, or whatever. I think it is human nature to always look to the bigger once you get something.
I have been eying the 84 even though I know I can get by without it---so, honestly, I would make that list, then call Ben Lang. Believe me, you will be impressed with his personality. He will steer you in the right direction once he knows that you have an idea what you want. You know, if money is an issue and you really want the bigger model, ask Ben if he has any demo units, its winter, he may surprise you. 20 years ago, I got sick of using a hammer, so I bought nailing guns, well, the Lang has done the same thing for me in regards to cooking.
How was that? Think Ben will give me a deal on an 84 now? HAhA