Both of the engines will be just fine, but I would be dead set on waiting until more mileage and road use data come out on the new 7.3.
I wouldn't have chimed in again other than you mentioned using the NEW 10 speed trans. So one first year design is ok as long as it's not the engine? What were the comments from your 6.2 group about new transmissions? You may hear, "well, transmissions are different". All that other tech on the truck will sooner leave you stranded. More computers, more wiring, more complexity and then a more simple engine design. It's like we are arguing backwards.
Tried and true means lessons learned. Any problem the 6.2 could have the 7.3 can have. They aren't even trying to use crazy tech, it's a overhead valve push-rod V-8, it's just big displacement. It's what Ford considers the perfect displacement for the volumetric efficiencies they are looking for in lower RPM operation naturally aspirated.
All I am saying is to just wait and see about the 7.3 and that you may make a mistake. I'll also say just to go drive one. And drive one with 3k in the bed. Your auto broker shouldn't have a problem with this if they are any good. Before I ordered mine, I borrowed a G56 Cummins for the weekend and did what I expected to do with it. I pulled a skid steer at 11k pounds, I loaded 3800 in the bed and drove around. Maybe I didn't tell the dealer I towed like that... Go make your choice out there and stop listening to both sides of the equation in here. My local rental yard would love to help test a new F350 7.3 gasser and would be happy to load the bed to 3500lbs.
If you come back and say, "guys, the 6.2 was hands down better when the truck was loaded and I got X mpg over the weekend which was Y better than the 7.3." I'll agree with you, until then I'd want to get all my information before making the decision and you have a rare opportunity with a new engine being released. We won't be having this conversation in 2 years, your truck would simply have the 7.3 option by default for all the reasons you listed for the 6.2
Resell on this super loaded "small engine" truck should also be in your mind. This will be like the 5.4 F350s/Excursions back in the day. Most people don't take the time to study and digest a decision and the lack of the "big block" will have an impact that is more than the cost of the 7.3 upgrade. You know, like I do, that most truck buyers are just looking at the max HP/TQ and towing numbers like they matter. I don't think we'd have 1000TQ coal burners if not.
So for me, more depreciation and worse gas mileage across the life of the truck would mean my wallet would slap me if I didn't think about the 7.3.
I can taste the regret I would have, but I just want to be an opinion on your shoulder that you weigh with all the other opinions. I consider the new vs. old argument as weaker in our current society. So much "have it right now" means that previous opinions mean less because the products change so quickly.