I don't think that this is necessarily true. In Europe we have night trains running between countries which of course also take 8 or 10 hours or more and they a

I don't think that this is necessarily true. In Europe we have night trains running between countries which of course also take 8 or 10 hours or more and they are more or less profitable. However an average speed of 200 miles (320 km) per hour is still a lot. Especially because you will have stops in between which of course means that the v_max must be even higher.