CSGO Full screen capped at 300fps +stutter with high-end PC

THEPASHKA · January 31, 2023

Whenever csgo is running in full-screen mode, (with custom resolution) everything is smooth and fps is above 700 on 3rd party death match servers and on Faceit etc...

But, if I open OBS on another monitor (not streaming just opened) it cuts the fps to 280 - 300 and adds minor stutters, and in-game fps can drop to 180.

When testing on "aim_botz" map for example, right after OBS is launched fps goes from 800-900 to 280-300 and in-game VAR jumps to 2 - 4
But! Only while playing on custom resolution (1920x1440), it does not cause any fps drops, stutters, or lags in native 1920x1080. But I need my custom resolution.

Similar behaviour sometimes happens (other application issues are not consistent) when playing and having something opened on another screen like Discord (with someone's screen demo opened) or a webpage with Faceit.
But only sometimes. I'm talking about a few game re-launches cycles and fps might be dropping because of Discord and another time because of Chrome

The following issue completely goes away, when running csgo at Full screen boardless or windowed, but that adds on input lag and game feels choppy

I feel like when the game enters the full screen, it caps itself to monitor's refresh rate of 280 despite G-Sync being turned off.
I have similar behaviour in Minecraft, in-game FPS does not go over 280 unless using OptiFine despite in-game V-Sync being turned off and G-Sync also being turned off in Nvidia control panel

Hardware:
R9 7950x
RTX 3080 TI (OC)
32gb DDR5 (5600) 2x16
CSGO is installed and runs on NVMe SSD
Main Monitor ASUS TUF VG279 280hz G-Sync (DisplayPort)
2nd & 3rd monitors are Samsung C24F390 (HDMI)

I have tried/made sure
G-Sync is disabled, both in Nvidia control (globally) panel & monitor config
PhysX is set to GPU
Screen Scaling is set to Display not GPU
I have tried different launch settings for csgo
All drivers are up to date

Screenshot 1 - shows csgo with OBS running on the same screen as the game, and the fps is 600
Screenshot 2 - shows csgo with OBS running on the second screen, and the fps is 305

Please help, I'm out of ideas