Yes, opalines and golds grow to the same size - same goes for all other three-spot (trichogaster trichopterus) color morphs.
Females do chase males around if they feel like it but it's usualy the other way round. Also, size doesn't realy make a difference unless both are the same sex though, of course, smaller fish tend to get bullied more over-all as they end up lower down in the hierarchy. Having said that, this isn't always the case.
Can you say which picture the brown gourami is that you were talking about (the one you thought was female but we said was male)?