I follow most of the boards, and general reports have been as follows;

FSD and sport springs - no issues, big improvement

FSD and Eibach - some owneres have reported bottoming, even with bumpstops cut down or Euro bumpstops. FSD's definitely don't like this- makes handling squirrely on large dips.Otherwise, good ride and handling improvement.

FSD and Neuspeed - more owners are happy with these than the Eibachs, but a couple have reported the same phenomenon.Otherwise, the same.

These are not hard facts - just what I've read. It was enough to keep me on stock sport springs for awhile. I'd like to be lower for appearances, but it's not a race car, and it's nice not to worry much about scraping .
Lowering is about the same on both, I think; about 1 1/4" - 1 1/2" down from base.

 

Hesaputz, You had stock springs and FSD? What did you think? Was FSD a big improvement? Did you notice an improvement in handling and a deficit in ride upon switching to sport springs?

 

No, I started with S Line (sport) springs. I only replaced the shocks, and I found improved resistance to roll and dive, less jounce, better ride,and an overall more solid car compared to the stock shocks. Not night and day, but a worthwhile and substantial improvement. I'm very happy with the feel of the car, and I'm a road racer (Porsche)used to tight handling and response.I wouldn't use FSD's for track, but they are really nice for street driving.