For me Windowed or Fake Fullscreen doesn't change anything. It's even worst.
When it's quiet onscreen I'm around 22-25 FPS at 1920x1080 VSYNC Triple Buffered, High Setting but some visual effect disabled.
I'm on i7 8GB ram Nvidia 750M
I'm not expecting 60fps, but I would hope to get at least a stable 25 FPS. WHile moving or fighting it's down to 10-15 FPS