Kansasracer: there would be a small weight difference of course, with the Graphite version coming in a little lighter. But unless your running on carpet with foams(which I of course know we don't
) then you really shouldn't notice a BIG difference. The graphite chassis will certainly put more importance of getting the suspension set correctly, because it will flex less.
Personally, I don't think the differences are that big if someone is trying to save a little money by going with the S1 version.