for the stiffest spring I would cut some SRT springs. The Voughtland springs are similar to Eibach springs except the Voughtland don't lower the back as much as the front which gives a slight rake to the car. the interesting thing is that the car seems to have very little understeer now which is great. I personally think my car would look a little better with more rear drop and I was thinking of using the thinest rear spring pad.