I think it's really difficult to average 200-250 km/h over 1,000 km with a train. I would guess the trains that average that speed would be much shorter trips.
Various Shinkansen lines average that much or higher for long stretches. To be fair, there isn't a 1000km line in Japan, but ~500km at those speeds should indicate that it's possible. Sanyo runs at near maximum operating speed (300km/h) for most of its >500km run.
We don't have such train lines that do that much kms. We have fast lines, like max 600km. Longer lines have trains who are +180max. And each trip is like 7-8 hours.