The Elden Ring stutter work was unrelated to this effort, it was work in vkd3d-proton by Hans-Kristian Arntzen as part of our open-source graphics effort.
I would keep in mind that the results reported there are likely quite a bit lower (in terms of CPU-side performance) than what you could achieve in practice, because it's running all of x86 Steam+Proton in the emulator. In a pre-configured environment (like SteamOS for ARM), the Steam client and Proton itself would be native ARM code, and emulation would stop at the win32 API boundary (or at certain critical libraries' APIs if you're using Linux apps).