from the internet, i used this method.
Open a Terminal Window Enter the following command to see what your current setting is:
defaults read -g com.apple.mouse.scaling
This will return a numeric value. To speed up (or slow down) your mouse tracking, you can simply change this number accordingly by typing the following command, replacing the “your_mouse_speed” with a new number such as 5.0. Notice that read has been changed to write: defaults write -g com.apple.mouse.scaling your_mouse_speed The maximum mouse speed on mac desktops is 3.0 (when maxed out in system preferences). I changed my speed to 5.0 for my 24″ iMac and it was noticeably better.
defaults write -g com.apple.mouse.scaling 5.0
You may need to restart your mac to see the changes take effect.