I installed a set of Roush rear springs on my 05 GT yesterday. These springs lowered the rear of my car 7/8". It sits almost level and the tire to fender gap is now the same for the front and rear. This is exactly what I wanted and I like the level stance of the car. I've only driven 20 miles so I haven't really explored the handling but the ride seems very close to stock.

I have a question for anyone that has Roush springs. They are progressive rate springs and the lower rate coils at the bottom of the springs are fully compressed on my car. There is no gap between the coils. Is this normal?

 

I think I found the answer to my question. The "lower rate" coils are probably inactive coils that keep the spring in contact with the spring perches when the suspension is fully extended. I hadn't seen this before.