The ten-day schedule for Beijing, Xi'an, and Shanghai is very consistent. The key is to use high-speed rail in places that truly reduce the hassle, and to keep at least half a clear space in each city.
Let mid-tier cities change travel speed
Xi'an shouldn't be just a stop at the Terracotta Warriors. The city walls, hui fang, and nighttime streets are worth giving plenty of time to catch your breath between two major cities.
Don't treat High-Speed Rail Day as Attraction Day
On the day of the ride, you can arrange a nearby dinner or a short walk, but don't cram it into a full museum itinerary. Honest planning helps avoid accumulated fatigue.