Increase Bandwidth:

Microsoft reserves 20% of your available bandwidth for their own
purposes like Windows Updates and interrogating your PC etc

Snatch it from Microsoft:

Click Start then Run and type: gpedit.msc .This opens
the group policy editor.
Navigate to Computer Configuration/Administrative Templates/Network/QOS Packet Scheduler and then to Limit Reservable Bandwidth.

Double click on Limit Reservable bandwidth. It will say it can't be
configured, but the truth is under the 'Explain' tab i.e."By
default, the Packet Scheduler limits the system to 20% of the
bandwidth of a connection, but you can use this setting to override
the default."
So the trick is to enable reservable bandwidth, then set it to zero.