I don't feel like the V6 offers that much advantage in economy when not towing. It probably doesn't do quite as well with economy towing. There's too little reason to not just go with the larger engine options. Penny wise, pound foolish.
I towed that weight trailer on a cross country trip with the same weight you have. I did it with the Ecoboost 3.5 in an F150. What a pleasure that trip was! I could just about drive as if I didn't have a trailer. A year later, since I knew my truck was capable, we moved up in trailers to twice the weight. I didn't have to buy a new truck again and saved a ton. Don't underestimate how things change.