I'm a born and bred Northern Territorian, and up here we've gone through some changes to speed limits.
Until about beginning of 2007, we had open speed limits (yes, go as fast as your vehicle could safely go!) and on all the times doing trips out side of Darwin, there were some people who would do the odd 160 - 180kph in some of the faster cars, but people mainly stayed around 110 - 120kph.
Of course there were the clowns out there who did testing and raced quite fast, I've seen Lambos, Ferraris, Porsche all going quite fast: (guilty, I took out my dad's cbr1000 and raced a mate on his bike past the Boys in Blue at about 200kph and they just looked on as we were not speeding - open speed limit.)
However, after 2007 the government brought in 130 as the speed limit and now EVERYONE tries to do that in all types of cars, which is NOT safe...4WDs, trucks, sh!tbombs, caravans. My family owns a property about 120kms outside of Darwin which I visit a fair amount and every weekend its the same story - everyone trying to do 130, no matter what vehicle they are in.
Interestingly enough, due to the increased (yep increased) fatalities after speed limits were brought back in, the current government is looking to bring back open speed limits to some parts of the highway.
http://news.drive.com.au/drive/motor-news/open-speed-limits-for-territory-20130508-2j6zy.html I wouldn't mind - get to test out my toys legally and safely, key word being safe.
At the end of the day, everyone needs to be in a safe environment and not put others at risk.
An old Nissan Patrol with flogged out sussy, steering and brake components doing 130kph is a lot more dangerous than a 2012 911 Porsche doing 180kph.