A running 8.1 is about 1500, a cam, headers, and a tune will have it making 400 rwhp and over 500 ft/lb, on 87 octane.
My tune only truck is 320 rwhp through an Allison, and get's around 12-13 mpg being daily driven and weekend hauling.
In my opinion, the 8.1 is the best bet for plopping something in wherever a small or big block will fit, feeding it 87 octane, and lugging heavy thing's around.
6.0's can't come close in towing, and a set of injectors for a diesel costs more than an entire 8.1 replacement.
Just my opinion, if I won the lottery, I'd totally have a CUmmins Square lol.