What effect are you after? Are you looking to decrease body roll, lower for appearance, etc. Are you willing to have a harsher ride? Are upgrading shocks/struts in your future?
If you are looking for increased performance I would suggest something in the 700-850 range for the fronts and around what you have for the rear(250). The Steeda Street/comp springs will put you in this range. It will lower the car a little, but not much. I don't know a lot about the Tokico shocks that Ford has used, but an upgrade might be a good idea for the future. That should take away some of the body roll and offer a fairly stiff ride.
If you are just looking to lower the car, the Pro-kit will be fine, although the FRPP "C" springs may be more cost effective and give about the same drop. On top of that they offer close to stock spring rates and their made by Eibach anyway.
Hope that helps.