Maxing out BF4 on a GTX760 is not possible @ 1080p.
Need a considerably better card than that.
Whoever is maxing it out is either lying or not playing at 1080p. DO NOT TRUST YOUTUBE.
To answer your question. At the moment there is nothing that is truly capable of using DX11.1 other than a few small tweaks.
So no. Just for that I would not get windows 8.1.