Remember also that if you have a huge useful load, you have to have someplace to put all that stuff. A 2007 Allegro has a huge useful load, but a tiny baggage space limited to 22lb I believe. So unless you are hauling two fatties, you really can't use all that weight anywhere except the seats.
My CTSW has a lower useful at 585lb, but I can take people up to 260lb each (seat weight limit), up to 34gal fuel, and up to 110lb baggage. Good load that is VERY flexible. If it's just me I can take full fuel that will get me 800+ miles and 110lb of bags (plus another 70lb in the seat). Me and the wife can use 24gal and 70lb of baggage, plenty for a trip up to a week or so and still giving ~450 miles range with an hour reserve fuel. Me and a heavy friend, I can still take 24-30gal fuel and no bags for day trips.
My only point is don't just look at the useful load, look at where you can put how much in each location as well.