I had a 92 GTS. That hull/body design is very stable. I never even came close to flipping it even when making sharp turns at high speed. No worries. The decal on mine said combined weight of people and cargo not to exceed 490 pounds.
yeah when they add the vents in the back and the 717 in there it went up a bit. i've had me (200lbs) my dad (330 lbs) and my ex girlfriend(130) on it plus fuel and everything was fine. it was really tippsy and took some time to get on plane but it did just fine.