One thing to keep in mind is that you could run a 10 inch spring but it's just not needed with the amount of shock travel available. As long as the spring is not coil binding, you are fine. Spring rate is a whole different discussion. My new rear springs will hold up the car with NO pre load. Even my stiffer fronts needed pre loaded.
Here is a look at new vs. old springs. You can see the amount of settling.(Disregard the rear springs as I went from a 12 to a 10)
