I took the high speed train from Chengdu to Chongqing a few months ago and it was so quick I barely had time to get comfortable, like less than 1,5 hours from buying the ticket to getting off at Chongqing station.
A few weeks ago I went from Hue in the middle of Vietnam to Hanoi on a train and it was literally never faster than 60 km/h twice the distance but it took like 16 hours, Vietnam really needs to suck it up and ask China to build their railway up.