With the large map I think the high speed trains are really going to start making sense – They’re “only” three times faster than the 1850’s era trains, and just bridging two towns along a river feels like such a long way.
And sharp turns and all the slopes are going to slow those down a lot too – The extra speed on straights will let them catch up to the timetable. Keep in mind that goods and passengers are only willing to travel a limited distance/time before they go elsewhere.