I'm thinking of going with a upr Kmember kit but trying to figure out which spring rate would be best suited for my car. Its a HCI single T70 that makes a little north of 500/500. I will be running 90/10, 50/50 and eibach drag launch springs in the back with an airbag. I just weighed the car and it weighs 3100 lbs. The car will be used for mostly street use, but I race quite a bit. I'm leaning towards the 12" 200 lb spring. Any advice/input appricaited...