Hi!
I had limited connectivity problems and also a slow wlan on my surface pro 4.
Wlan always got disconnected from time to time.
I now installed windows 10 from Usb Stick and installed an old driver for wlan and it seems to be working so far.
I also set the registry value for TxAMSDU to 0.
I think the thing that helped was reverting to an old wlan driver.
I took the one from the Driver Package for Surface Pro 3 (January)
I downloaded it from Softpedia and it was named Microsoft Surface Pro 3 Tablet Firmware/Driver January 2015.
I Deinstalled the driver an then manualy added it via "choose from a list on driver on computer"The Driver Version is 15.68.3073.151
Hopefully it helps someone, since i have been trying to fix this probleme for days...
Kind regards,
Leonhard