H&R for non-GTI = part no. 29261
H&R for GTI = part no. 29176
29261 drops a GTI around 10mm from factory ride height. Perfect with Bilstein B6 or B4 for those having to deal with Serbian farm tracks.
29176 drops a GTI around 30mm from factory ride height. Perfect with Bilstein B8 for those blessed with smooth roads.
As for the spring rate differences, who knows, H&R don't publish them. I suspect the non-GTI H&Rs will be softer than GTI spec.
You might want to cross reference the coloured paint blobs on your factory springs to confirm they are actually GTI spec first. It is assumed that GTI, GT TDI, GT and GT Sport all got the same shocks and springs (the common theme being 'GT' = sports suspension), but worth finding out for sure before spending any money.