You're being a little vague so it's impossible to analyze.
However, if your average speed is 25 mph and the average doubled to 50 mph, I'm sure you'd be happy. With maglevs, we'd probably want more express trains.
My point is that top speed is only relevant when a train can reach it. If a train stops every two miles or less (like mine does in the morning), the vast majority of the time is spent accelerating, decelerating, or stopped.
Rolling stock acceleration is specified & designed based on requirements which is based on passenger safety & comfort (especially on regional / intercity trains) rather than rolling stock constraints: https://link.springer.com/article/10.1007/s40864-015-0012-y
Modern "diesel" trains are diesel electric, outside of large freight trains the motors don't really strain to accelerate.
> If the top speed is 160 km/h, then a good EMU has a stop penalty of about 45 seconds, a powerful electric locomotive about 135 seconds, and a diesel locomotive around 190 seconds. With short dwell times coming from level boarding and wide doors, EMUs completely change the equation for local service and infill stops, making more stops justifiable in places where the brutal stop penalty of a locomotive would make them problematic.
For example, I'm visiting the Bay Area this morning and Caltrain (diesel locomotive) has acceleration much lower than BART (electric multiple unit). Acceleration here is determined by what's practical with the equipment, not the maximum forces people can currently handle.
However, if your average speed is 25 mph and the average doubled to 50 mph, I'm sure you'd be happy. With maglevs, we'd probably want more express trains.