I haven’t tried local and express trains on the same station because there are only 5 platforms on one station, but in separate stations, people likely to ride express trains.
Also note that acceleration is much more important than maximum speed for shorter lines, especially for later game. I’ve tested a speed race for BR 103 (200 km/h) with RABDe 12/12 (125 km/h) on same line which is longer enough to bypassing 2 adjacent towns and RABDe 12/12 wins! BR103 even can’t hit maximum speed of 200km/h and its actuall max speed was about 160km/h. That was a surprising result.