I agree with power being a funny animal. And, a lot of people lean towards what "feels" the most powerful when pulling a load. The most powerful thing I have ever hauled with (granted, it wasn't a pickup), but it is the same exact concept, was my old Peterbilt. Modified 565 isx cummins, would head out west on i-10, out of san antonio going through Kerrville area, some big 7% grades, grossing 88k, and would hit those hills at 80 at the bottom, and crest them doing 75, no downshifting, just cruisig in 18th gear. The truck was quiet, even with 7" straights on the inside, smooth, and didnt feel like it was doing anything. Super deceptive, flip flop that theory with my old w900l, with a 550 cat, that had the exhaust and turbos screaming, and felt like it was working for all it was worth, and really getting it done, would pull those same hills at 60.
Ive towed with a few 6.4's, pulled my triple axle enclosed car trailer with a cc dually I almost bought, and it was quiet, smooth pulling, and felt like it always had power on tap, ready to be used. If I was wanting a tow pig that would go long distances with a lot of weight behind it, I would want whichever truck offered the plushest interior, with the most creature comforts, while handling the weight the best, and deal with power as it is found needed. If its a big heavy trailer, it would be a '09-'10 f450, with the 4.30 rear end, I drove one that was a king ranch, and the rpm at 70, was only like 2300, but the 19.5 wheels, and heavier rubber and the bigger brakes are worth it IMO, compared to whats on the new 450's.