XopenGL is the worst for fps, D3D9/D3d11 are the best.
- Turn off gore
- Turn off Decals
- Turn off Dynamic lighting
Or if you like decals just turn off gibs, or vis versa having them both on can drops fps badly even on newer pcs, combogib spam maps at least.
I could play at 1920x1080 ~ 144 fps. with an I5 2400 IGPU, the same with an i5 3450.
If your pc has a pcie slot keep an eye out for 2nd hand GT1030 you can easily get 300fps 1080p even with nicer graphic settings and you won't need power cables for it, if you are patient you can get them for $20-$30 if you are lucky.