年をまたいでしまったが、なんとか解決したようです。Ken Thomas さんによると、
CrossOver does manipulate the sensitivity of scrolling, but makes no attempt to manipulate the speed of mouse movement.
You can issue the following command in a Terminal window, when CrossOver is not running, to disable even the scroll acceleration changes, in case it somehow is responsible for the problem you're seeing:
defaults write com.codeweavers.CrossOver DisableScrollAcceleration -bool NO
(The double negative is correct. Normally, scrolling is accelerated. CrossOver disables that acceleration when a Windows app is frontmost. By setting the value to NO, you are telling CrossOver not to disable it. That is, to leave it alone.)
開発元はやっぱり対応が速いなぁ。