How much to drop the car depends on what you like. The prokit is 1"-1.5" and is lower in the front and higher in the back, if you like it real low get the sportlines about 2" all around, get the H&R's if you like a nice even drop bout 1.75", get air bags if you like it slammed, but I think that's kind of ricey. I got the Eibach prokit, the drop is so subtle you couldn't even tell my car was lowered (unless you knew how high it was with stock springs). It's perfect for me now because I have a Roush side exhaust. If I were you and I had the $$$, I would just get a complete suspension system rather that just change the springs. And the stang up there looks like H&R's to me.
the sportlines are a nice looking drop, however I have found that they throw your Roll Center WAY too low. I have them with the X2 Ball Joints and it still does not handle like I would like.