Abmario :
I have shifted from Windows 7 to Windows 8.1 since Jul-Aug, (never get BSOD so far).. I can see the difference between the two..
Windows 8.1 uses less system memory. Boot faster in windows 8.1 8-10 sec vs 30 secs of Windows 7 (both SSD)... Boost in fps when it comes to gaming..
here are few threads for references:
http://www.tomshardware.com/answers/id-2091185/windows-gaming-performance.html
http://www.tomshardware.com/answers/id-2043400/windows-windows-gaming.html
Those threads you referenced as proof are nothing. They are posts by people with little to no credibility. Single post wonders. However, despite that, in ideal circumstances it IS somewhat accurate. Not to the degree expressed by a few driveby members, but enough to warrant mention.
Anyhow, there is some performance gain in windows 8.1, if you don't have driver issues with older hardware. Gains generally run from between 1-6%, which isn't that much, but is consistent, depending on the GPU and game title. And here is an actual review, for reference:
http://www.hardocp.com/article/2013/11/24/battlefield_4_windows_7_vs_81_performance_review/#.VEi3Iul0xhF