Spring rates

Now that I have been driving on the Eibach coils and Racing Beat rear swaybar for a few months, I'm trying to decide what my next suspension mod is gonna be. The car handles much better now, but is still heavily biased towards understeer. I was considering adding the Racing Beat front swaybar, but a larger front bar is just gonna make the understeer worse, my thoughts are going towards springs. At this point, I think that Ford gave us a much softer spring rate than the Mazda6, especially in the rear, and this is causing the heavy understeer problem.

So my question is, does anyone know the stock spring rate? According to the measurements I took of the stock coils the rates are 198in/lbs front, and 126in/lbs rear. Then I made a call to Eibach and their coils are 20% stiffer than stock, so that would be 238in/lbs front and 151in/lbs rear.

What I'm trying to accomplish is to see if there would be anything to gain from using springs for the Mazda6 since their stock and aftermarket springs seem to be much firmer.