Mines lowered 35mm all round on g-max running 195/45/15's - had to get a set of spacers (5mm) on the front but thats because the offset of the alloys was out slightly.

I know of a few people running 15's and a 60mm drop at the back with no problems apart from the usual slight arch scrubbage over bumps etc. Don't know what the score is at the front thought - IMO 35mm at the front is really the max you should go - im already having problems with garages to take to car for the MOT as theres not enough clearance for the ramps