ICE test train reaches speeds of up to 405.0 km/h

Amdahl's law in effect - which is the reason trains in Germany top out at 300 and most at 250.

Re-read it, as I didn't recall it properly: [0]

"the overall performance improvement gained by optimizing a single part of a system is limited by the fraction of time that the improved part is actually used"

[0]: https://en.wikipedia.org/wiki/Amdahl%27s_law

Thanks for the quote, Germany has (too) many stops on the ICE lines (often for political reasons) and those are the limiting factor, not the top speed. The best train in Germany is Berlin->Frankfurt, not because of the speed, but the "Sprinter" version does not stop.

There's another factor in HSR speeds: track degradation and maintenance. If you run the trains faster, they cause more wear to the tracks and require more frequent maintenance, and also tolerances on the tracks need to be kept tighter. Germany already seems to have trouble doing maintenance on time, so running trains faster would make this worse.

Yes, the German rail services prefer to build huge new trains stations instead of better tracks. We're waiting for 120->160kmh for years now, always promised, always moved to the future.

And probably the tear is bigger on curvy lines which most lines in Germany are, compared to e.g. China.