Or you can use fholger's excellent FSR modded openvr_api.dll
Not only you can boost the frame rate, scale up the rendered image, you can also set the sharpness.
For my GTX1080, I use NIS to scale up the image (2x). The effect is better picture and color with similar frame rate.
Give it a try, you will like it.
The other plugin developed by fholger, openvr_foveated. Doesn't do any improvement, and the frame rate drops. So I don't recommend it. Maybe someone else find it useful for his own case.
It also comes with sharpness feature.