It would all depend on the other mods that you have. If you are stock or mildly modified (CAI, exhaust, tuner) then you won't see much gains in going to a true 85mm TB, however you'd see some gains by moving to a ported TB. However, if you had headers or started looking into internals like a cam, then you'd want the 85mm.
No, you would still see gains without doing internals, but you need to match your tb choice to the mods you have, going too big can hurt your bottom end but you'll see gains in the upper powerband. You have to look at where you want to make your power.
So I don't do much towing, thinking about taking it to the track just to see a few things and get some ideas, normal everyday driving and commuting to work are the basics of the truck. Diablo and catch can arrived today will have those installed this weekend. Looking into headers and still debating on which ones. ARH is just too far out of my price range. So with those I should stay with the smaller TB and get more out of the bottom end than go with the big daddy?:doh:
Looking at those mods you'd want to stick with a stock 80mm butterfly, so look at the ported TBs. Moe's has a good port profile and the fastman TBs have been around for a while with great results as well. You want to maximize your intake velocity with your mods, so stick with the ported TBs.