There is a difference between the Roush Springs and the Eibach springs. I know because I have Eibachs (with Bat Stuts BTW), and RoushSC had a Stage II Roush Cougar which has the Roush Springs. He also did replace the stock struts with BAT struts. I've driven both cars and I have found that the Eibachs ride a bit nicer. Its because the Roush springs have a constant k (spring rate), while the k for the Eibachs is variable. What does that mean? It means that the Eibach are softer while under light load and stiffer with more load, while the Roush springs are stiff all the time. That's why Eibachs are more expensive.
My $10 worth
