The obvious answer you can find everywhere is:
defaults write .GlobalPreferences com.apple.mouse.scaling -1
which disables mouse acceleration, but locks you at one sensitivity.
SmoothMouse no longer works. Mouse Acceleration Preferences Pane and SteelSeries ExactMouse both behave the same as
com.apple.mouse.scaling -1 at all tracking speed settings (but without restart required).
Is it possible to disable mouse acceleration while still being able to adjust the sensitivity?