An excuse to impose limits was all the road deaths, which were from drunk driving. That'll stop the drunks, fining them for speeding.
Most people drive to where they feel safe anyway, save for the odd idiot... Most people did around 90kph on unlimited roads in the NT.
I see it here in ACT, there's a few places where it's 80kph and people do 60kph (state circle in particular). But, despite this, people still smash into the guard rail on the off camber corner on Adelaide Avenue. Lowering the speed limit won't change this.
As soon as Australia changes its attitude to safe driving practices the better. Less text book drivers and nanny state limits and more skill and responsibility taught.