The performance impact for that setting is horrible and I would like to see them add that screen geometry into the game so we can leave that setting off and enjoy the full rendering performance of our graphics card instead of also letting it render the screen to a parallel projection surface.
I found this topic helpful, I got a decent and reliable performance boost balanced with very good visuals, which is a much better trade off than I had previously managed myself.
Basic idea: "Problem is when you upsample x1.9 or x2.1 for example, you will have MUCH blurrier picture. When u upsample EXACTLY x2 u have clear picture and much less artefacts."
Requires manual settings in your personal SteamVR config (don't confuse with the default which will be overwritten with updates), so I put a steplist for the 5k+ here: