Our 182 P model... IFR and STOL equipped.
Empty weight: 1815.9
Useful load: 1134.1
80 gal @ 6 lbs/gal = 480
Full fuel useful load : 654.1
We've looked at doing the paperwork STC for 3100 MGTOW but there's a limit to it in real world practice.
If we are trying to haul lots of stuff, climb performance suffers. If we don't mind that, it can be used to lengthen the legs back out and/or carry a larger fuel reserve. But...
There's also a considerably low weight limit on the baggage area in the aircraft limitations that isn't based on balance, it's based on structural limits, so you really have to put the majority of the weight in or under the seats. Or in the fuel tanks.
There is a very small space under the rear seats of a 182. Not large enough for most luggage. Nothing useful up front either. It's going in your lap.
With four people on board, if I recall correctly, each can have a 37.5 lb bag (150 total pounds) and then you are maxed out behind the seats, unless they'll put it in their lap. I'll have to go check that. But not right now. Tired. It's close.
We ran into the limitation once and realized that even getting another 150 lbs of crap in the back, would be difficult. We've had the back seat and the rear area maxed out before with stuff piled so high you couldn't see out the back window. Unless your load is dense, you simply run out of space.
Don't get me wrong. It'll carry a ton of crap. But when you switch from two people to four, they don't want their luggage sitting in their lap. And you hit the baggage area limitation. STC or not.
Plus... You're stuck aloft if you don't have an emergency and decide to land early. You must be below 2950 to land, even with the STC.
Obviously in an emergency you'll just land and have someone inspect the aircraft. But you have to watch out for legs that are short if using the STC as a way to haul more stuff.
If you're using the full 150 lbs of the STC for additional fuel, you also technically need to carry more. 150 lbs plus legal reserve. And you're eating into reserve as soon as you've burnt down enough to legally land. Maybe you want a little more.
Honestly the STC doesn't give many scenarios so many great options that it's always worth doing. You need to run the numbers and just decide if shorter legs will get the job done with less restriction. It's a juggling act.
So far, we haven't had a scenario where the STC would actually be worth it. We just hop in smaller hops with an hour reserve, and keep hopping.
We pretty consistently fly at 9000-9500. We see 11.5 gph as an average over multiple years.
Lower altitudes, 13 gph.
0-3000 MSL, 15 gph.