i recently discovered that the Gnome/GTK window manager/compositor doesn't disable properly for fullscreen 3D unless you install Gamemode. my video card was released end of 2023 and i never saw it do much better than about 70fps on the most demanding games, but now it sits between 90 and 120 most of the time on the same exact games, and the flow (because of frame dropping before) is out of sight smoother now.
for FPS and other high action games (like maybe parcour or bullet hell types of games), the FPS matters a lot. anything under 50 starts to impact your ability to respond to the maximum of your capability. raw framerate doesn't matter as much as the lack of frame drops. oh yeah, variable sync also helps a lot because vsync increases latency by one frame.