Go on the Eibach website, it say something like 20-25mm I think but all I really can qualify is that the drop on Sportlines is as far as you'd want to go without rubbing and bumping. I'll post some pics when I get a chance but the front tyre sits almost on the wing rim and so does the rear. Looks well low to me but it's what YOU want at the end of the day. The Gti is'nt exactly high to start with so this drop makes a big difference.
The handling is still really good too and doesn't bump-stop or rub and handles really well, only thing now is some new anti-rolls and some new bushes.
For me any lower for road use would just be a nightmare to drive on anything other that the Rockingham Speedway short circuit.
Pics coming this week, but sure someone else has done this already.