macOS Sierra: Increase mouse cursor speed beyond System Preferences maximum
There are 2 FREE ways to accomplish getting mouse speeds over 5.0 accelleration on mac OS High Sierra:


First, is by executing the command-line:


defaults write -g com.apple.mouse.scaling  X

where X is the amount of acceleration you want in the form of a number with one decimal space after it, then logging out, and logging back in. 
Therefore if you wanted to increase your speed to 8 acceleration you would type in the terminal the following command:

defaults write -g com.apple.mouse.scaling  8.0

Note: If afterwords, you adjust the mouse controls in System Preferences again, you have to once again enter the terminal command and log out to regain your accelerated mouse settings.


Second, is to use an app called mousezoom. It gets installed in preferences pane.