>>78591530
The reason you can't do that in GUI with Xfeces is because Xfeces is very slow at modernizing. They only accepted GTK3 in 2018 or 2019, and first release was in 2011 or something. The same thing can be said about libinput, the new input driver, which was released in 2018. Same thing (as of 2019, I didn't use desktop environments in 2020) Cinnamon, Budgie, Unity... pretty much everyone except GNOME and KDE.
I hope you are open-minded and this little issue won't make you think that GNU/Linux is bad on desktop (which it is, for some people at least, because they have their own necessities such as Photoshop which they use to earn money).
Mouse accel in GNU/Linux is actually very similar to Quake 3 mouse accel. Many people who played Quake 3 like mouse acceleration, because in Quake 3 it was linear acceleration and was highly customizable, just like in GNU/Linux now. See https://www.youtube.com/watch?v=SBXv0xi-wyQ for more information or just read the links in description if you don't want to watch the whole video.
Anyway, type [code]xinput list[/code] in your terminal. Then, you'll see lots of devices. One of them is your mouse name. See its ID? Now type [code]xinput list-props mouse_ID[/code]. This should list all properties your mouse has. There are two of them which are important. First is "libinput accel speed", second is "coordinate transformation matrix". Setting accel speed (with [code]xinput set-prop mouse_ID prop_ID -1[/code]) to -1 should remove all acceleration (which I don't recommend myself, set it to around -0.85, it's good trust me, I literally can't play osu! and quake without acceleration after playing that). The coordination matrix property has lots of different numbers that are divided by commas. The last one is the only important one (for mice. Others are important for touchscreens and tablets). It sets the speed your cursor moves. So, to set your mouse to half the speed it does now, type [code]xinput set-prop mouse_ID prop_ID 1 0 0 0 1 0 0 0 0.5[/code]. To make it 2 times faster than standard speed, replace 0.5 at the end with 2.
Now, libinput actually detects what DPI your mouse has and calibrates accordingly so that every mouse you connect to your computer behaves the same way and moves at the same speed, for consistency. Currently, I don't think there is any way to set it to 6/11, besides calculating it yourself (which I don't know how to do). 6/11 doesn't matter anyway. Most games allow you to turn on raw input which lowers the input latency and isn't affected by settings in the system you're running, be it Windows or Linux or MacOS.