JwBtw, I was testing 8k for fun earlier and on an MGE server with 2 players there was 0 noticeable stuttering, but when I switched to a 6s pug it started stuttering. So idk what is up with the engine.
I can only guess its because tf2 doesn't do a lot of splitting CPU tasks between multiple cores, so when you are in an MGE server, there is a lot more CPU headroom for your 8k polling, but 6v6 pushes your CPU too hard that 8k doesn't work well. I think more modern games can perform mouse input calculations independently from other calculations.