I don't think tank size will make a difference, I had mine in a 75 gallon.
Here is a quote from Animal Planet
Social Behaviors:
The Gold Gourami are generally considered a good community fish when small, but they are not as peaceful as the other gouramis. They have been known to attack smaller fish. When they get older, only keep them with fish their own size. Individuals will show varying degrees of aggression. Some will be very belligerent and will handle their tank mates quite roughly. Others will be peaceful to the point of shyness. The aquarist should be prepared to adapt their tank to suit all personality types.