In Melbourne I live right under one of the approach paths for the airport. Not departure, I'll admit, but aircraft noise is not an issue.
In Sydney, I have a flat which is under the departure tracks from 34L. Some aircraft are noisy (the older 747s, and surprisingly some of the A340s), but others are very quiet. The RR engined 380 stands out here (but not the alternative engine). The upshot is that I'm sure Sydney could have some modification to its curfew to make it a bit more flexible.
But, the biggest issue is the total lack of flexibility that exists with regard to curfew adjustments after weather issues. Storms that more or less shut down any of Sydney, Melbourne, or Brisbane, have their effects magnified many times over by this lack of operational flex.