Yup, but only the OP knows what size his people are.
Also, note that for the theoretical 500nm trip, the difference in available cabin load was only 60 pounds between the Mooney and the 182. As you know, on the average you're going to have a headwind. Because the 182 will be exposed to that headwind for a longer period of time because it's slower, as the headwind increases the available load of the Mooney will approach and then eclipse that of the 182 (although they'll both be going down).
Meh - There really aren't any 4-seaters where two "real-sized" people are going to be comfortable for that long. I've had four people in the Mooney for maybe an hour at a time, I've had four in the 182 for a couple of 3-hour legs but they were my skinny brother and sister-in-law. If you want four real-sized people, a PA32/PA34 sized plane is a lot better.