Re: Directx 11 fps drop
Of the thousands of posts I've seen for this game, this is only the second time I've seen someone suggest DX12 is an improvement. LOL
Thanks for posting the DXDIAG report straight off. Also, you've taken some good, proactive steps to try to resolve.
If you're looking at FPS, you likely have at least 1 overlay on. I suggest disabling all overlays and check FPS in-game.
According to the DXDIAG report, you have multiple issues going on including a memory issue. (Look at the last section in the report.) I would look into those.
One thing to check straight away - make sure your memory speed in BIOS matches what your CPU/MOBO can handle. There are numerous posts regarding these being out of sync and causing issues. You might even try disabling XMP, if that's on.