It's very unlikely you will be stopped at the airport. If you attempt to re-enter Australia then you may have some issues.

You could write to them and explain your situation and also that you were flashed 4 days in row etc. Although, given you were traveling significantly above the speed limit, they will probably take a dim view.

While speed limits in Australia do seem to change more frequently than Italian PM's, vast, straight stretches of dual carriageway aren't usually prone to it. If you plan to use that as your defense, then you should probably make sure you have some pretty good evidence of it.