The SSL system has a couple of advantages over the standard set up. If offers a comfortable ride with good handling, it has a rising rate second spring and is adjustable for both ride height and correct fitting.
The priority with the standard SSL kit is towards a comfortable ride however if someone wants a more "sporting" ride and handling they do also do a race kit. I am told that a higher rated spring can be provided on request. The softest spring from the race kit would probably be appropriate for fast road use but I have not tried it.
I am sure similar results can be achieved with careful selection and fitting of appropriate parts however I consider the kit fitted to my car well worth the expense.