In China any flights that take around an hour (around 700km of land distance) would probably be better traveled via HSR. Flights that around 2-3 hours long usually make more sense compare to HSR, although I know people who would prefer train as long as it is anywhere under 6 hours.
- Even the busiest security lines in a typical HSR station say during holidays would take 10 minutes tops. Regular weekday or weekend the security lines take about 2 minutes. They don't scan you very thoroughly, liquids are allowed, don't ask you to take off shoes belts or scan laptops, lithium batteries etc. They're usually just checking for weapons and explosives.
- HSR gates typically close 4 minutes before departure and the gates open about 12 minutes before departure. If you factor into security you rarely need to arrive more than 20 minutes before your actual time of departure. For flights, most people do well to arrive at least 40 minutes before departure otherwise you would be cutting it close.
- In the case you miss a particular train usually you can wait 30-60 minutes for the next one. If you're desperate there is standing room.
- I have almost never encountered a delayed train but flight departure delays happen nearly 30% of the time, factoring into things like weather. And when you are delayed it can be for hours.
- You can order takeout between stations and it is delivered to your seat.