Generally when I have to jump out with 3 guys, it is about 5" (about 2"-3" above my ankle). We will be gently rubbing/gliding along the gravel. Small gravel isn't the issue with that much water, it's the bigger rocks that stick up 1"-2" above the rest. If we have those, we just get out, or else it will be like bumper cars, bouncing and spinning off rocks. The bottom flexes quite a bit as well, which helps going through the shallow stuff.
It would also depend on how much weight is in the boat, including gear and anchor(s). Centering the weight is key too. Having too much on one side, even slightly, will definitely cause the boat to ride a few inches deeper on one side, rather than when it rides level. Keeping most of the weight, or heaviest guy in the front, always helped a ton as well.
3 guys on Pine Creek and Loyalsock during trout season was never an issue. I wouldn't take 4 though.
Mike
Mike