What is frame time?
Frame time is how long your PC takes to draw one picture. It is simply 1000 divided by your FPS. At 60 FPS each frame takes 16.67 ms, and at 144 FPS it takes 6.94 ms. Frame time tells you more than the FPS number because it shows how smooth the game feels. A steady 7 ms feels better than a jumpy average.
Why upgrades give less and less
Going from 30 to 60 FPS saves 16.7 ms per frame. Going from 144 to 240 FPS saves only 2.8 ms. That is why the first jump feels huge and later jumps feel smaller. If your screen is 144 Hz, FPS above 144 only helps by lowering the delay a little.
What is a 1% low?
The 1% low is the FPS of your slowest frames. If your average is 144 but your 1% low is 60, you will feel stutter. Many players aim to keep the 1% low close to the average. In CS2 you can show a frame time overlay with the console command cl_hud_telemetry_frametime_show 2; see our CS2 command list.
Which FPS cap should I use?
With G-SYNC or FreeSync, many players cap a few FPS below the refresh rate so the screen stays in its variable range. Without variable refresh, you can match the refresh rate with V-Sync, or run uncapped and accept some tearing for lower delay. Test what feels best in your game.