For the diff tightness usually the tighter it is the more traction it will have....to a point. If you run the front diff tighter it will pull more out of corners but give up a little steering on corner entry. Rear diff if its tighter it will not really allow the car to rotate very well though the corner....but will give more traction once power is applied.....so it could cause the car to push comming out of the corner when on the gas.