It's hard to answer because having towed with Cummins for years now, there is no question it's better.
Could I get by with the 6.4 gasser in a 2500? Absolutely I could. When I was given that opportunity to tow with that Power Wagon it towed well. But it was no Cummins.
The 6.4 was notably light in the nose with the tongue weight I'd put on it with my 2100 lb car trailer and the 4300 lb Dakota I put on the trailer. I could feel a notable difference in steering and ability to maintain a straight line (tail wagging the dog) on the highway due to the lack of the weight of the Cummins up front. Off the line was understandably "sluggish" compared to the Cummins........ but nothing that would make most drivers hate towing with it. It's just hard to give up the towing prowess of the Cummins.
Given the prices of the two trucks - as I recall, the loaded Power Wagon was $64K. They weren't willing to deal on it like they were for the Cummins....... so it really was a no-brainer to stick with the Cummins. I didn't need lockers, a winch or electric disconnecting sway bars. Beyond those off road features, they're very similar trucks save for the engines.
Pretty sure the Cummins gets better gas mileage overall than the Power Wagon too, at least when towing.
I think the 6.4 will win the un-loaded drag race.......but not by much. 4:10's in the Power Wagon and 3:92's in the Cummins and the weight differences keep it close.
I believe the 6.4 trucks recommend premium gas as well. Could be a notable difference in towing with one on 85 octane vs 91.
So, given the amazing deal I got at Brandon Dodge when I traded my dually in on this 2500 I haven't looked back at the 6.4 trucks. But there have been a few occasions where I've missed my long bed 3500 dually truck. You can't beat the length, weight, leaf sprung, traction that those trucks provide when towing. But I DO NOT miss the dually for daily driving. The 4-link, coil rear suspension of the 1500 and 2500 trucks makes such a huge difference in the comfort of the unloaded commute.
Whew........ guess I got a little word-smithy there.
