Hi Tim,
I'm by no means a guru, but through bitter experience, I can tell that with the popping outfit you have, I suspect you are likely to experience some serious wipeouts from bigger GTs. My brothers and I started with outfits/line classes similar to the 50-60 lbs gear you mentioned, on our early trips to the Whitsunday area, and over a number of demoralising years, got comprehensively dusted by GT's more times than we care to remember. Given their tendency to dive straight down, they are a very difficult land-based opponent, and just through line angles, will often brick you even without taking any line. We've found that even a 15-odd kg GT is tough to land if fishing land-based with that sort of tackle. And the area you talk of has plenty of fish twice that size. For that reason, we have upped our tackle to GT Special rods and Stellas filled with 80 lbs (absolute min) or preferably 130 lb tuffline. We adopt a rather savage fighting method, and the fights are over quite quickly, whether the battle is won or lost.
But as Pete mentioned, there are plenty of other critters you can expect to have some fun with if you target the rocky corners, close bommies as well as current lines, fish like trout, spaniards, longtails, queenies, etc will all be possible at various stages if you persist with poppers and stickbaits of various sizes. For those species, the tackle you have will be adequate, I reckon.
I, too, have not specifically fished Hamilton, our efforts are based 10-20 miles south of that area, but you might want to send a pm to Cy & Kerrin Taylor, who seem to have their fingers on the pulse of the northern Whitsundays.
Cheers
Angus