is it worth it in the new stang or are the factory springs and shocks any good ? or should i just add the 1 airbag ps thetirerack has shock&spring kit for 640 i dont think it has a airbag with it http://www.tirerack.com/suspension/suspension.jsp?&make=Eibach&model=Pro -System+Kit&group=Pro-System+Kit&autoMake=Ford&autoModel=Mustang+GT +Coupe&autoYear=2006&autoModClar=&partNum=35101.780&perfCode=S