Here's how I did this.
1. Unlock the final Express Train.
2. Upgrade BOTH stations so they have an empty track connector each.
3. Build a track connecting the two stations using the empty station connectors and build it as straight as possible using bridges and tunnels if needed to keep it as straight as you can. Avoid making too many corners but if you have to make them long as this will help the train keep up its high speed. Also make sure no other tracks connect to this as you don't want other trains running on this track at all. More trains, more delays.
4. Don't forget to build enough supply towers along the track as you don't want it to slow down from running low on water. A few seconds at the supply tower will save weeks on the journey.
5. Once you've built this select the fastest express train and connect the two stations. But before running it go into the trains options and prioritize passengers then select a maximum of ONE carriage. You might have to do this with both stations but you also need to select the new track on this same page (Track 4?).
Then let the train go and wait a few moments. Doing all this should get the train up to about 100mph and be the fastest train in the whole of the Down Under.
On a side note, it cost a lot of money to do this so have several million at hand (maybe save it before doing this as the route makes very little money for the cost)