The major higher speed limits here are 80, 100, 110 and 130 kmh.

110 only occurs on major motorways ... and there are other roads around these. They also have more than one lane .. so overtaking a slower vehicle should not be a problem.

130 only occurs in the Northern Territory. It used to be unlimited. But people would travel around 120 .. as that is the speed the road trains travel at and most don't want to over take or be overtaken by them. These roads are one lane in either direction and fairly straight... most people won't over take you unless they can see some miles into the distance! The other thing people learn here is that speed = fuel, fuel is not cheap and the fuel stops are a fair way apart. Unless someone else is paying for the fuel ... people slow down.

80 is the nominal speed of grey nomads (travelling retirees) .. they find this is a good economical speed (fuel, tyres etc) and they have no need to get somewhere fast. You may also find this a good speed, if your not in a hurry. And yes they travel at this speed in the 130 zones. The do have UHF CB radios and communication between them and the truckies occurs, both understand the position of each other. You might find picking one and sitting (say 500 meters, there is a lot of space in Australia - use it) behind it a good idea.

General 'rule' of speeding ... most people consider going 10 kmh over the speed limit is ok. Except in Victoria where 2 kmh over may get you a ticket, or at a fixed speed camera ... these have signs before them .. so if you are inattentive them you may get caught. If you want to be certain of not getting a speed award .. stick to the limit, or to the speed of the traffic.