the ball diff incorporates spacer plates allowing you to adjust the spring tension which of courts affects the amount of action in the diff. review the ball diff set support doc which has diagrams of this explaining the effect of each tension setting.
also, i forgot to mention that you should probably reduce your steering angle to reduce roll, the softer the compound, the greater the reduction. you won't get a very tight radius with a reduced steering angle but at speed, the car will turn on a dime.
