250kph with about 200kph average. Johor toll to KL toll in 1hr 45 mins.
180kph average if driving at night since most places of NS highway got no street lamps.
But with the increasing amount of traffic, getting much harder to do so, unless you are trying to get killed. Have slowed down a little now since a last incident when a truck going maybe 70-80 pulled into the outer lane without warning! Jam brake until smoke all around my car, and was maybe few inches from rear bumper of truck. When I arrived in KL, I found a strip worn from all almost new tires, and got to get them changed. Almost $2K gone!
If want to go fast:
(1) invest in great brakes & tires
(2) in a light car, make sure good aerodynamics, otherwise go for heavy continental cars. You cannot imagine the turbulance force when you overtake a coach/truck when doing more than 200.
(3) you better be super awake & alert. reaction times needed are very short
230km/h in a fully race tuned little Toyota Starlet, from Benjamin Sheares to Changi airport at 3.30am. I used to ply the streets every Friday and Saturday night looking for other chio cars to race. Made lots of friends doing that. I started alone but that soon grew to a big convoy of supped-up cars plying the streets every Fri & Sat bullying other chio cars, who we usually end up being friends with. It was a great time of my life.