Jurinko,
I have followed your advices :
- SSLR, SSAA, SSAO : OFF
- shadows high, terrain shadows default
- Power service : OFF
and things got way better. I kept MSAA X4, cockpit illumination ON though. Just tried removing the tiny bit needed.
FPS increased to around 100ish.
But it still lacked the "butter smooth" feeling I needed, specialy when I turn my head quickly.
I followed the advice from another thread and capped the FPS of DCS to 60. My monitor is currently running @ 120Hz.
And now, it feels really smooth with quite high graphics settings.
In case it can help someone in the future...
Arnaud's post in 3080ti + 3840x1600 : what should I except ? was marked as the answer