You are always going to make more (net) money in a USA major than you ever will in Australia.
Australian majors pay a lot better than US ones, there's no doubt about that. I know you've got the higher taxes and costs of living in Australia, but I'm still doubtful whether you are always going to be better off in the US.
With that being said, I wouldn't be too excited about moving to fly in Australia though, it's not like the Australian aviation industry is exactly booming.