All the highway limits varies between 80 to 90 km/h depending on
various locations. Take note, coz if you travel at 100 on a 80
stretch, you'll be about 20 overlimit.
While these are hard limits, enforcement-wise unoffically depend on
the TP whose path you suay suay come across. Usually up to 10
overlimit, they close one eye. About 20 overlimit then chances are
they enforce.
Enforcement on the roads are usually more strict when the traffic
is light, like between 11pm and 7am. So be more careful when
driving in this period.
But having said these, law sez these are hard limits and drivers
who decide to play the close-eye margin will be lan-lan should the
TP want to enforce at these hard limts.
Hope this helps, Cheers! 
