Ignore the IshiirukaFX part. We don't support that.
D3D12 is still experimental, that is correct. For nvidia GPUs though you should use OpenGL. It is extremely fast on nvidia and D3D12 only beats it marginally in most cases, a healthy amount in a small handful of games. OpenGL is also a hell of a lot more stable and D3D12 may be getting dropped in the future.
Anyways, to simplify admin89's post:
If you want to have the ideal image quality and performance, set IR (Internal Resolution) to whatever IR is closest to your display's resolution.
Then set anti aliasing to 2-4x SSAA.
D3D12 is still experimental, that is correct. For nvidia GPUs though you should use OpenGL. It is extremely fast on nvidia and D3D12 only beats it marginally in most cases, a healthy amount in a small handful of games. OpenGL is also a hell of a lot more stable and D3D12 may be getting dropped in the future.
Anyways, to simplify admin89's post:
If you want to have the ideal image quality and performance, set IR (Internal Resolution) to whatever IR is closest to your display's resolution.
Then set anti aliasing to 2-4x SSAA.