GTIs only have one part reference for H&R -30 mm springs.
Eibach sells Pro-Kits (will only lower around 10-15 mm) and Sportlines (will lower around 30 mm). The Sportlines are very similar to H&R -30 mm, but you'll notice the rear a bit higher than the front, compared with H&R springs.
You can see pictures from Sportlines (initial pictures) and from H&R -30 mm (last pictures) in my Ed. 30 project.
I have Eibach Pro-Kits in my GT Sport. It rides much higher.