Mark has covered most of it, but I will add a few comments of my own based on trial and error during a lot of GT trips in local waters.
I use a Saltiga S-Extreme 4500, initially with an FCL Labo 81MH, but after nearly busting my back a few times on big fish with this rod, I bought a Carpenter BLC83/40 - a huge improvement as far as fighting fish goes. A lot of people will think this rod is too light for big GTs but this prompts the first question:
How big are the GTs that you are regularly likely to encounter?
I only say this because it is a waste of time running heavy gear all the time if you rarely need it, because it will wear you out and you will not enjoy using it. Like using a 30lb outfit for fishing for bream, just because a jewie might jump on.
I am happy to be undergunned on the rare occasion, because for the other 99% of the time, using a lighter outfit is enjoyable and not tiring.
I initially chose Jigman 65lb which was great for casting distance but I got a lot of wind knots. I tried reducing the amount of line on my spool, didn't help much. I put some 100lb Torx (old spool a mate gave me a few years back) on a Saltiga Surf as an experiment and while I had no wind knots, the distance was reduced by about 20-30%. It was a good exercise though because although the reels are completely different, it did feel like the heavier and stiffer line was easier to manage while casting.
So I wanted to get 80lb tuffline but could only buy 65lb locally, so I tried that. Initially I did get quite a few wind knots but after reducing my line capacity a little bit on the spool, AND reducing the length of my 130lb mono leader to a 2m length, I rarely, if ever, get wind knots now.
If I was setting up from scratch though, I probably would go 80lb tuffline or a good quality braid like Varivas, with the 2m leader and slightly underfilled spool.