Personality of the fish is certainly a major factor but really, it is just one of many factors. A lot of other circumstances and factors involved in any community tank. Sex of fish, age of fish, all the other tankmates and how they fit into a pecking order, decor, territories, ect. ect.
Anyways, IME, twice, I have had large male GT's in a cichlid community tank and both were very aggressive fishes, but neither were very capable. With CA, GT's were very low in the pecking order ----about the only CA fish their size they could push around were nics. And the GT's bullied smaller fishes; whatever they could push around.
I had a problem once, with a male GT and two oscars, all of similar size and weight -----around the 6-8" size. The GT wouldn't stop chasing them so I removed the GT for some time and then re-introduced it. At first it looked like the same thing all over again, but finally the oscars started to stand up to it. The GT fought both oscars and got his butt kicked twice. The oscars never had a problem with him again. After that, the oscars got huge quick, and the GT eventually got to about 10" but always remained subordinate to them.
If I were to house these two fishes again in the same tank, I'd give the oscars a head start. I know oscars have a far superior growth rate, but still. Young oscars can be very wussy ---- they need some age and size to be able to defend themselves. Oscars can make very good bosses for a tank. Given my experience with male GT's, I sort of suspect if you end up with the GT as a boss it might be a reighn of terror.