That has very little to do with the ICE train itself though, which can do above 320 km/h just fine in regular service (on international connections though, since in Germany the global train speed limit is 300 km/h I believe).
While the high-speed tracks in Germany are indeed quite a bit of a patch-work, there are over 1000 km of track certified for >= 250 km/h (as of 2015; quite a number of more lines got finished since then, but I could not find the updated number that included them) and by now really rather long corridors are very high-speed.
The route from Munich (south of Germany) to Berlin is now mostly covered with upgraded routes for example.
I think the 4 hours for that route are quite competitive to Shinkansen times.
The fastest Shinkansen route (from the listed operating speed the only one that actually operates at 320 km/h; all others only operate at 260-300 km/h) is the Tōhoku Shinkansen line, which takes 3 hours and 20 minutes for the same distance traveled.
While the high-speed tracks in Germany are indeed quite a bit of a patch-work, there are over 1000 km of track certified for >= 250 km/h (as of 2015; quite a number of more lines got finished since then, but I could not find the updated number that included them) and by now really rather long corridors are very high-speed. The route from Munich (south of Germany) to Berlin is now mostly covered with upgraded routes for example. I think the 4 hours for that route are quite competitive to Shinkansen times. The fastest Shinkansen route (from the listed operating speed the only one that actually operates at 320 km/h; all others only operate at 260-300 km/h) is the Tōhoku Shinkansen line, which takes 3 hours and 20 minutes for the same distance traveled.