railinrx8

I am looking for some information about after market springs. I want to upgrade the springs but cannot go to a coilover setup at this time. Does anyone have any info on the following.
1) What are the stock spring rates front and rear?
2) Of all the spring kits available, which ones increase stiffness the most?
3) what are the spring rates for this kit front and rear.

Not so concerned how much it drops the car but mostly on the spring stiffnes (rates).

Any help is appreciated.