Install imwheel: sudo apt-get install imwheel
Edit the default settings: sudo nano /etc/X11/imwheel/imwheelrc
Add the following to speed up the scrolling system-wide. Note: this does disable the option to use ctrl+scroll in your browser/editor to change font size:
".*"
None, Up, Button4, 4
None, Down, Button5, 4
Now edit /etc/X11/imwheel/startup.conf to auto-start imwheel when you log in by changing IMWHEEL_START=0 to IMWHEEL_START=1.