I've endlessly searching for a solution around this, the issue seems to points to win 8.1 upgrade. I am trialing one tip I found, to reset and roll back the intel driver to the factory windows one. Go to device manager > network adaptor > update driver > find files from my computer > find from list > choose driver supplied by 'Microsoft'.
Driver version of the windows one is: 16.0.0.62
The wifi is now connected as 130mbps, a little slower than the intel driver, but it seems to provide more stability to my wifi connection. Will test more and report back in.