My VDSL speed is 20-21Mbps, according to the installer that's due to the far distance from the house to the "terminal".

By reading the Official requirements of the Netflix, "a steady 25Mbps connection" is needed. Thus mine is lower than that. 

But Netflix also quoted "up to 7GB per hour", which calculated as 7*1024/3600*8=15.98Mbps. Thus mine is just enough.

I can stream 4K on Youtube with barely no problem, of course the buffering is quite bit of slower than FHD. 

Thanks, guys.