wifi performs 1/2 speed compared to windows10, compatibility issue?

Hi, all

I'm using a AC router and a disk attached to it. usb3.0 or eSATA, sharing via smb.

Copy files from router's disk using 5G wifi, speed is always about 55 MB/s when switched to bootcamp windows10.

Copy files from router's disk using 5G wifi, speed is always about 27 MB/s when switched back to native El Capitan.

Copy files from another PC using 5G wifi, speed is always about 60 MB/s when using El Capitan. (seems wifi works almost ok?)

when option+click wifi icon, The Tx Rate shows 867Mbps, PHY mode:802.11ac (may be this means network is working as expected?)

Is there a common wifi driver issue or compatibility issue with smb?

And how to debug/fix this?

Thanks.

PS. copying files using ftp protocal, the speed is about 60MB/s.