tire stretch isn't too bad. I'm lowered with H&R super sports.
Did you just have them installed? They should settle more, unless the super sports I have just go pretty low for some reason. Or if MkVI spring applications specify different lowering amounts.
What are the wheel/tire specs?
Edit: Should've looked first. P/N's are different for MkVI Golfs and GTI's, as well as MkV GTI's.
Mine lower 1.9" all around (1.3" on 08+'s with Euro ride height), P/N 54752-77. Assuming you bought 2.5L/TDI super sport springs for the MkVI, your drop is 1.8" F, 1.7" R, P/N 54756-77. MkVI GTI's drop 1.5" F, 1.4" R, P/N 54758-77.
I'm going to guess that the spring rates are different as well.