Having done half a dozen suspension upgrades on my various offroad vehicles, my recommendation is to to target a specific deficiency and figure out how to fix it. In your case, an extra inch of lift in the rear via simple spacers would give you ~200lb of extra weight capacity before the rig appears to "sag," without stiffening the ride like most aftermarket springs. And it will cost you maybe $150, professionally installed.
Now, I won't pretend we also don't want our vehicles to look good. If you also want it to look relatively level, then yes, you will have to go with stiffer rear coils, but your offroad ride quality will suffer. My previous 4Runner had ~600lb of permanent armor and gear, and I followed the standard "XXX springs for YYY additional weight" guidelines. Sure it didn't "sag," but it rode like a hotwheels car and had my kid's head bobbling around like a rag doll on mild offroad trails. I redid the whole suspension, losing about an inch of lift in the process, and ended up with a cadillac offroad ride through which my kid could nap as I lifted tires.
Bottom line, don't let yourself get wrapped up in which upgrades are "best," but focus on specific deficiencies.
