I’m running CachyOS (based on arch) and it is blazing fast. Both with Firefox and Vivaldi. Especially compared to the windows install I used to have on the same machine. Or is your point only about windows?

Hmm, I'm using the CachyOS kernel but on NixOS. What CPU/GPU are you using?

I tried using the flatpak Chromium in case it was some NixOS build optimization oddities but didn't see much of a difference.