Originally Posted by b1m9t0

As a guideline, there is a tolerance of 10kph above the speed limit before you may get in trouble.

The two main speed limits you are likely to experience are 50kph and 100kph. So generally you can travel up to 60kph and 110kph respectively and not get in too much trouble. (This tolerance drops to 4kph over public holidays / long weekends and the entire December-January period).

Also there are provisions to fine drivers who drive too slowly and hold up traffic, however this is rarely seen and enforced by the police. Other drivers tend to get extremely frustrated and may attempt unsafe passing manoeuvres if stuck behind a slow driver, especially (as mentioned above) when some stretches of the main highway can go upwards of 50km without dedicated passing lanes.

I do urge that if you tend to drive slow (anything less than a constant 95 in a 100 zone) to pull over and allow other cars to pass where possible.