Having just driven from Brisbane to Melbourne, I can tell you that if one get caught for speeding, one deserve all one gets.
Speed signs all along the pacific Hway and Hume.
I my self believe that 100 klms per hour is fast enough. With out the van on, I set the cruise control on 100 klms. In one hour I have covered around 100 klms. That's good enough for me.
Remember that most accidents are caused from speed and fatigue. Imagine the disaster if we are on 120klm speed limit.
Plus our road network and conditions are not condusive to high speed. Some people will still travel over the speed limit be it 50 Klms or 120 Klms.
Slow down stop and revive and survive is the best motto for drivers.