Apple mouse scrolling is too sensitive in Yosemite

Question

I've use a wired USB Apple mouse with scroll ball (A1152) on my iMac 27", and since upgrading to Yosemite, the mouse scrolling has been way too sensitive and doesn't allow any fine adjustment of scrolling speed/acceleration in system preferences. In the Mouse preference pane, the 1st position on the Scrolling slider is way too slow–a full scroll of the bar down moves about 1/4 of a full webpage at native resolution with very slow acceleration. The 2nd slider position is not any faster than the 1st. The 3rd slider position accelerates way, way faster, and scrolls a distance of about 8 full pages using a moderate flick of the scroll ball. At this high sensitivity, I need to scroll fairly carefully to move only one page. In a finder window with 500 items, it accelerates fast enough to move from top of the list to the bottom with less than one full finger swipe of the ball at moderate speed. Any setting from 3-8 on the Scrolling slider is the same speed and acceleration and is way too fast to use in a well-controlled manner. The behavior system-wide and is the same in any browser (Safari, Firefox, Chrome). This is nothing like how it behaved in OS X Lion through Mavericks over the past four years. Also, I can set the scrolling slide to the 3rd position, close system preferences, and go back in to find that it has set itself to the 2nd position, but the scrolling behavior is that of the 3rd position until I move the slider again.
I've trashed some .plist files from ~/Library/Preferences/ that I thought would reset things (com.apple.driver.AppleHIDMouse.plist and others) upon logout/login, but the behavior persists. I've tried a few pieces of software to try to override mouse settings, and while they will affect the mouse tracking speed and acceleration, they don't work well at controlling the scroll speed. I've reset the PRAM and SMC. I've created a new user account. Nothing has allowed usable adjustment of scroll speed/acceleration of the Apple mouse.
Any suggestions on how I can regain in Yosemite the usable adjustment of scroll speed/acceleration that were in all previous OS versions would be appreciated.

Answer 1

Try setting the scroll wheel scaling manually, by running the following command in the Terminal and then logging out and then back in to re-load the settings:
defaults write -g com.apple.scrollwheel.scaling -float VALUE
In this case, try values of 1, 0.5, 0.25, etc, decreasing in half each time to see how the scroll wheel sensitivity responds, and then use the one that works best. Alternatively, you can use the system preferences to set the sensitivity to the two values you have used so far, followed by running the following command between each to see what the value is for each:
defaults read -g com.apple.scrollwheel.scaling
Then you can determine some intermediate value to use, and use the first command above to set it to that value (again followed by logging out and then back in so the value will load).