I must say from trial and error, the 700's in the front, and 800 in the rear is the ticket. Never go below this in my opinion. As far as the best springs in the world, Hyperco first choice, no doubt, Eibach second.
If you plan to track the car, I guess a bit more, but for street the above will give the perfect ride. Adjusting the valving on the Motons or what ever you have, will fine tune the ride, but going to low on spring rate, only makes for a sloppy driving car. You would be surprized that going to a stiffer spring will often give a better ride. Soft springs are compressed into a range when hitting bumps in the road, that make them very harsh. Think about it for a moment. Take your everyday family car, and load four people into it, well the first thing you notice is the car my be a bit more stable, but it rides very ******* the bumps, as you are no longer in the spings optimal ride position. The factory has set the springs up on the car for optimal ride, considering between one and two passangers. A half ton pickup truck will actually ride a bit better with some weight in the back, as those springs are most optimal with X amount of weight on them. This is exactly what happens when we go to low on the spring rate. The compression and dampening in the shocks has a simualar effect. Spring and valving, and the car's weight must be tuned, and have little room for error.
Make sure and order the size spring the coilover is intended to run. If you don't you can't adjust the coilover properly without altering the piston travel. I do believe that a longer spring can travel more distance without changing it's lb rate as much as shorter spring, but the body of the coilover dictates how long of a spring you can use.
