Could easily be the DX11 change causing that issue. THE CPU being at 100% is the limiting factor for your FPS. Have you tried another game that is DX9/10 and not DX11?
Do what Walkerie said and that will prove if its the change in DX version, which will be using a lot more power from your system to render the slightly shinier things. Make sure HBAO hasnt turned itself on, and that any other DX11 only features have turned on now they are available.
Do what Walkerie said and that will prove if its the change in DX version, which will be using a lot more power from your system to render the slightly shinier things. Make sure HBAO hasnt turned itself on, and that any other DX11 only features have turned on now they are available.