I have mouse sensitivity at max, still too slow.
Once the game bugged for me and it didn't hide my desktop mouse cursor and I got some interesting feedback how the mouse system appears to work behind the scenes.
I maybe totally wrong, but it seems that the game calculates delta of cursor movement between each frame update. When the FPS was high, the delta, for me at least, was very small. The game frequently snapped view to the cursor position and reseted it to the center of the screen. Because the FPS was high, this snapping occured very often and looking around was smooth, but painfully slow due to the small deltas. But when the FPS dropped, I saw the cursor travel further between the snapping and the game calculated higher deltas and looking around was faster than on high FPS, but jerkier. When the FPS dropped to very low (1-5*) the movement was way too fast, because I was accustomed to the extremely low response and the game counted very big deltas between the infrequent frame updates as I was swinging the mouse around.
In other words, the game appears to have a very peculiar way of doing mouse on Linux and it is varying on FPS and very likely on mouse DPI as well.
Hopefully this gets fixed at some point. If needed, I can do some testing.
* I will take this opportunity to thank the dev team for optimizing the particle count etc of the game. I no longer hit these extremely low FPS numbers.
