Re: Below 20 fps

Hmm, thanks for the detailed post. I see you've already tried the DX12 toggle.

Can you run the performance monitor while you play (if you play in Windowed you can swap more easily) and see if that gives any hint at where there might be a bottleneck. 

https://technet.microsoft.com/en-us/library/cc749115(v=ws.11).aspx