I am looking at the Steeda adjustable height rear spring seats for my track day 2011 Mustang GT. It will allow me to change spring rates easily as it accepts standard 2.5" coil over springs. I'm also hopeful I'll be able to use the height adjustment for some corner weight adjustment. I'm currently running fixed length Ford "K" rear springs spec'd at 199.5 lb/in (tested by Vorschlag at 221 lb/in). which has lowered rear of car approximately 1-3/8" (Driver side) to 1-1/2" (passenger side). I want to use either a 200lb/in spring or a 175lb/in spring. I've found softer rear springs allow for increased weight transfer to the outside driven wheel increasing traction off a corner. My question is has anybody used this set up and if so what length coil over spring have you used? I've had recommendations of either a 10" or 12" spring. I'd prefer to order correct length spring first time to avoid hassle of buying and changing springs. TIA