Legend! Thanks for the guidance!
No worries, basically you need to find the original openvr_api.dll (rename it to something like .old) and then copy the new one in. Mine was in the x64 folder.
Then open the toolkit, look what the keys are set to, then during the game pull up the menu. If it appears, you know it's working.
In testing, the Nvidia NI scaling seems pretty decent, couldn't really tell any difference at 90% scaling. I had 40% sharpening added on.
Then I did a custom fov render, think it was 50% at 1/2 and 80% at 1/4. It really dropped my GPU load, and it looked almost the same as before.
Obviously I'd rather not do any of this, but if you are looking for extra headroom it's pretty great.