From my years of tuning, I change springs and dampers together as a set. If you really want your suspension to work right, the sets need to be matched. Also be advised that lowering a car can affect all sorts of things like bump steer, camber, caster, roll center, and other things that aren't so adjustable on a production car. I have a feeling that the best suspension kits will be the ones FRPP develop since they have access to all sorts of test equipment that the rest of the market doesn't have. The H&R coil over system is probably the best if you really want your car to handle well, but remember that too much lowering is very bad. Over the years, my Mustang went from really low to now sitting closer to stock. I had to bring the roll centers back in line, adjust bump steer, and find the right compromise for handling and tire wear. BTW, setting bumpsteer is not fun to set. Hours of work go into setting it.