A post to Allot Communications' blog, by Maya Canetti [pictured], provides an analysis on the bandwidth consumes for Window 10 upgrade:
"it amounted to 8% worldwide before the launch on July 29, 2015 (when it became available for Windows Insiders) and around 4% on the official launch day. There are two reasons why the launch was so smooth. For one, Windows 10 is just not as popular as e.g., Apple’s iOS 7. Secondly, Microsoft did not rollout Windows 10 at once, but in stages.
.. Microsoft has embedded its “Windows Update Delivery Optimization” (WUDO) technology in Windows 10. Instead of relying on operators to schedule updates (as was done before), WUDO by default uses Windows users’ bandwidth to deliver Windows 10 updates and apps to all connected devices that are running Windows 10. The peer-to-peer patching technology is similar to BitTorrent.
The impact of the staged Windows 10 release on networks bandwidth consumption was notable. The graph below, which was taken from a mobile operator during the period of July-August, clearly shows spikes in bandwidth on July 16, the prelaunch of Windows 10 to Windows Insiders, and on July 26, the official Windows 10 rollout".
See "The Hidden Snag in Windows 10" - here.