If you don't find a way to set it in the GUI, i do know of the way to do it on the command line, this command will do what you want:
where 3 is the acceleration, and 1 is the threshold, if you supply only one number, its taken to mean the acceleration. Setting things to the right values is mostly trail and error until you get what you want. More threshold means you have to move the pointer farther before acceleration takes effect, giving you more fine grained control. Acceleration is how fast to move once it kicks in, the more, the farther your pointer will go once it goes past the threshold.
