I have red the forums extensively before ordering a GTI myself, and deliberately did not put a pano roof - too may complaints and rattles. Even the dealer (this was my 2nd VW from the same guy) pulled me to the side and told me to not get the pano roof.
The M135 is awesome car, it could probably be my next car, as I really want more horse power, and the M135 is around ~12k Euro (~10k pounds) cheaper than the new R, at least in my country (we have regional pricing here), all specced out.