Well, I would clarify the 'always full and weight restricted' comments. I flew this route twice a month for mostly the past two years (until ORD base took it over....). Although the flight is often full'ish.....there were days with 80-100 open seats. When the locals see that, everyone and their uncle lists to non-rev, so you will see 50-60 on the non-rev list....mostly buddy pass riders (and many who never check-in or show up).

The weight restrictions can often be mitigated, and I would say that in my experience it was only as issue on perhaps 20% of the flights. HNL westbound is a cargo load issue. The flight will often show max weight, but when the cargo is loaded and 2,000 pounds disappears, we can get most if not all of the non-revs on. GUM eastbound is a runway climb limit. We could get more peeps onboard by doing a packs-off takeoff and mostly eliminating the climb limit issues. Always able to get out of both cities with full loads....and jumpseaters. But.....there is the occasional day when it all falls apart and maxed out is maxed out....
If you are going that far to dive, you might as well continue on to Palau via the flight out of GUM. Never went there, but everyone who did said it was much better than the diving on GUM.
Good luck!