I don't know much about cummins besides that owners like them, but digital engine usually offers better fuel economy than the older technology.
You plan to drive the truck for long years, so initial cost will be secondary, while difference in annual fuel cost can be significant.
My both 7.3 are stock and I've been pulling 30,000 + lb combos with my F450 just fine. Would I love 400 HP? Sure I would, but spending $200-300 on fuel daily is not making me looking for increasing this part.
Would I have 60 grands burning my pocket, I sure would take newest technology with power AND fuel savings, but the World is not perfect and looks like you figured out this part already.