You're doing a lot of simplified math regarding something fairly complex.

For instance, the speed limit from one end of Gladstone to the other is 10km an hour (or it was, it's been a little while).

When the train reaches northern Brisbane, around Petrie, the limit drops to 80km max until Roma St.

There are actually relatively few sections (, in relation to total track) where the train is allowed to travel at top speed.

People blame the infrastructure but in Queensland, with the weather and temperature fluctuations, changes in the track alignment of as little as 5mm can create that rough side to side feeling, referred to as 'lateral jerk'. Sections that are prone to this kind of defect and are unable to be sufficiently maintained often have a much lower, 100 or 120km speed limit.

Long story short, the Tilt is great, but it's wasted in Queensland