A Sun Cat would be good, a great choice I think. I can only speak from my own experience but my 5" male GT grew up with Corys, Pearl Gouramis & Fruit Tetras at different times & ignored them all. My 4" female is in with 4 1 1/2" Loaches. Their personalities vary so much it's hard to know what might or might not work. My male GT is in an 8' tank with an Oscar , a 3" female Severum & Silver Dollars right now and he gets chased every so often, he bothers no one and just tries to stay out of the others' way. But I've read about some pretty aggressive GT's. I personally wouldn't try Angels with them, but that's me. Angels are just too slow and those fins are too tempting to a lot of fish.
You might check planetcatfish.com for the Sun Cat, I think they get about 8" but I'm not sure, been too long ago that I looked them up.