I was under the impression that the Eibach's (and some others) had the variable tension in their springs to allow a kind of "best of both worlds" scenario - softer for light needs - smaller bumps, etc., and stiffer when really pushed. The stock springs seem to be just one or the other - stiff on the SRT-6 and soft for the other models.

Is that interpretation wrong? Assuming one is not interested in going to the track, is the only purpose of aftermarket springs to lower your car? I thought the idea was that you'd get better overall performance too.