As mentioned before, the file is in ~/Library/Preferences/.
But preferences will be found in more than one file.
.GlobalPreferences.plist
com.apple.driver.AppleBluetoothMultitouch.mouse.plist
com.apple.AppleMultitouchMouse.plist
com.apple.driver.AppleHIDMouse.plist
Note that .GlobalPreferences.plist is invisible.
Mouse speed is called scaling in .GlobalPreferences.plist.
Setting scaling past 3 with defaults write -g com.apple.mouse.scaling 5 has no effect immediately and may require a logout.
file://~/Library/Preferences/com.apple.AppleMultitouchMouse.plist
file://~/Library/Preferences/com.apple.driver.AppleHIDMouse.plist
file://~/Library/Preferences/com.apple.driver.AppleBluetoothMultitouch.mouse.plist
com.apple.mouse.scaling. Sodefaults write -g com.apple.mouse.scaling -float 5.0is what you're looking for. – Lucas Jul 07 '17 at 14:06defaults write -g com.apple.trackpad.scaling -float 5.0– Cave Johnson Jan 14 '19 at 20:27