I would go with the strano spring my buddy has them on his fiirebird and loves them. If you are going to do the mods one at a time I would go in this order,because it makes no sense getting springs that the shocks cant dampen correctly
1. sway bars front first( best bang for the buck)
2. shocks (koni, bilsteins, not kyb talk to sam about shocks
3. springs.
4 offset control arm bushings adds -.5 of camber you will want
5. a good diff
6. r- compound rubber

I would def buy from Sam he has tested on the 4th gen more than any body i know and is willing to share the secrets he has learned over the years. If you buy from him its a win win you get a winning set up and the years of knowledge is only a call away.