windows 7 runs on DX11 and windows 8.1 runs DX11.1 also win 8 is better at handling multi core operations. if your on windows 7 you can do some reading on unparking cpu cores. its quiet easy to do and you will see a noticeable improvement in bf4. personally im on windows 7 with unparked cores and the performance increase to windows 8 would be minimal at best