i think the KONI Sport adjustable dampers are better value...and adjustable. i find being able to adjust the 'rebound' to be great; can tweak to suit your personal preference and the roads you usually drive on.
i can only presume the FSD's may provide a slightly better ride (in terms of comfort), which may translate into slightly better grip in some conditions, but i have been happy with the Sport model. now my 3rd car with such ('94 MR2, '00 156 TS, '06 GT).
despite this and the cost, i still probably wouldn't buy FSD's over the Sports. of course, i'm biased, cos i haven't experienced the FSD's.