I have a GGC and a Halfmoon, for the most part they get along just fine.
They "use" each other big time for preening purposes :lol:. I can leave them together without concern, but that's not to say they don't have their spat moments, they're more noise than anything though, and very short lived episodes. The GCC is the aggressor when it kicks off, but the Halfmoon gives as good as he gets and it's all over in seconds. :lol: