Spring Questions....

Ok, So i'm looking around for used springs and i mainly see three types, but I'm a bit lost (big surprise) as to what will acheive what I want. I want the car to be a bit lower, and a bit stiffer. I don't want to be feeling my ass in my throat everytime I hit a bump. I will probably be going with the Koni adjustables, but if i were to find 2nd hand new or lightly used KYB adjustables or Tokiko Illuminas I might go that route if the cost is low enough. It all boils down to money. I think I want the Tein's and the Koni's, but it depends what i can jump on.Can anyone tell me if i'm understanding all this correctly? How big of a difference is there really between the tein and Swift springs in terms of stiffness; is 40lb that big of a difference ?

Starting point, my car seems to be about 13" from center of wheel to lip both front and back.

From my understanding the FM springs would be stiffest of my options, but would not lower the car at all. (318lb front/ 233lb rear)
http://www.flyinmiata.com/index.php?...t&sku=13-46500

Swift Springs are the softest I'm seeing soft. (196lb front/ 129lb rear)
http://www.trackdogracing.com/websit...prings_kit.htm

Tein Springs would be the *best* combo for me of lowering and stiffness (230lb front/ 170lb rear)
http://www.trackdogracing.com/websit.../tein.htm#tech