Automation is great but it is not, nor ever will, be perfect.
There are several things about the NG that I don’t like. One of them happens to be the tendency to over speed. I think Boeing is improving the software some. When we first got these things (NGs) we had many cases of crews over speeding coming out of altitude.
Sorry about the time off from work. It seems a little harsh to me; but then you are in China, it’s their airline, their rules, and their culture.
Hindsight is 20/20 so I will dispense with “you should have done…..” and “the manual says…..” and barking at you to “fly the airplane”. At this point it’s counterproductive, and the event is self-critiquing. There are known issues with VNAV in the NG. The NG will over speed in VNAV, the system is not perfect. Whose responsibility is it to keep this from happening; yours and mine (the folks who get paid to fly it). When the NG gets off VNAV PTH (does it frequently) and tucks into VNAV SPD it will over speed if given the opportunity, as you have unfortunately found out.
What did you have on the descent page, what cost index are you using? One suggestion would be to put in something like .76/280 in the descent page. Doing so should give you a larger margin. Another technique to consider is to start down early in VS (or “descend now”) and then transition to VNAV PTH.
I like the wings, engines, performance, auto throttles and the HUD on the –800. The flight deck ergonomics, 2-axis autopilot, elements of the FMS and the noise level leave a lot to be desired.