Why not go for a 3500 not hardly any difference in price and you will be set for you upgrade down the road.
I agree people always seam to think they are saving buy purchasing the 2500 or 250 vs the 3500 or 350.
When I had my F350 built, I priced out both. The difference was less than 5K, for a 53K truck that wasn't much. Considering the payload difference is significant. Now I was comparing SRW to SRW, I'm not sure the difference between a 3/4 ton SRW and a 1 ton DRW as we didn't want a dually
Another thing to consider is not buying off the lot. I purchased my F350 from the dealer custom ordered which meant the price was set before order, no dealer fluff or haggling. MSRP for the build with discounts rebates etc was 53K. I paid 41K, my friend just bought an F150 for 40K off the lot.
I'm not saying that it will always work out better, but if you find one on the lot that's close to what you want, ask the dealer to run a build, and make them run a build and price it out. You might be surprised, many times the reason is with the order they have no overhead, no lot storage, no test drives eating up fuel, no potential non sales. Truck shows up you pick it up, they are out nothing... Dodge is different however when I bought the Ford dealer showed me the build invoice and said we want $500, I agreed and they ordered the truck...when confirmation came back the price quoted was lower than actual cost, dealer only made a $136.
Of course aftermarket add on's, sealer, undercoat, etc. add to the dealers pocket but I was very satisfied. I actually priced out a build from more than one dealer and went with the one who was lowest.