I have a real problem with mouse lag, it affects the game so much and I just hate it.
I turned v sync off in the .ini file, I added a few things into the .ini that are supposed to help it.
I downloaded a performance mod, and turned down my settings to low.

What else can I do?

Turn down shader-heavy graphics options. If your video card can't handle the shader load, the render is delayed enough to cause what appears to be an input delay.

Queue