i lowered my mk3 by 40mm, and as u can see by my sig its quite low, depends on how much trouble you want to give yourself when u go over speed bumps etc mate.
I got my kit from GSF (tho its not one of there kits) Its a G&N one that was purchased from one of the guys behind the counter at the lincoln branch. I am very happy with the kit with cost me ?200, and ?100 to get it fitted.
Hope this helps
If you want some before and after pics let me know and i will email them to ya.