Low FPS in borderless windowed

[Aistaraina]

GPU: ASUS Strix GTX 970 OC
CPU: Intel i7 2600k
Running the DX11 client.

In Ishgard, on max settings, I get 30 FPS. If I switch to full screen mode, I get 55-60 FPS. I understand that you do take a performance hit running windowed, but it shouldn't be cutting my framerate in half...