New NVIDIA driver 11/27, better performance!

[Pseudopsia]

It's possible that's because your performance is already pretty top notch. Might be more noticeable the lower on the totem pole you are?

My GPU performance isn't bottleneck by the CPU so there's room for improvement. When I overclock my GPU I can get a score of 16000; multi GPU setups can get much higher.

I'm also running Windows 8.1, and I have heard that DirectX 11 gets boosted to 11.2 with the installation.

You're right when you upgrade to 8.1 you get directx 11.2:
Windows 8.1: Directx 11.2
Windows 8: Directx 11.1
Windows 7: Directx 11

Current FFXIV client is directx 9 so it doesn't utilize any from Directx 11 so higher directx version isn't going to increase performance. If you want to see directx 11.2 features you have to have a video card that supports it and a game that supports it. Nvidia's newest graphic cards support up to directx 11.1.

Support for new directx version is slow because MS reserves it for it's new OS and only newer videocards support it. So it's extra work for developers to support it for a small audience. It's rare to find a game that supports direct 11.1 even though it's been out for over a year. BF4 will support it:
http://en.wikipedia.org/wiki/List_of...ctX_11_support

Directx 11 client for FFXIV suppose to be 6 months after PS4 client. I have no idea if they will support features from 11.1 or 11.2.

I think support for DX 11.1 will increase rapidly for newer games because XBone supports it.