Counter point: The Aus driving tests don't prepare/train drivers for the current highway speeds as it is.
If we implemented a system like Finland's, where new drivers are actually taught how to handle vehicles in adverse situations and conditions then I agree raising the speed limit would be feasable.
But that would require a huge state gov investment in training infrastructure and that will never happen.
Also,
The current condition (and ongoing condition) of Australia’s primary road surfaces are unsafe even at the current speed limit.
The combination of poor initial construction, decades of neglect, bushfires, floods, abuse by speeding and overweight road users has resulted in a regional road network that is so far gone that the most cost effective solution is to tear up whole sections and start from scratch.