Okan, do I recall correctly that Mr. VdH set yours to operate with the 18g effective mass of the 4P?
@petek - It's worth pointing out the effective mass - earlier 11" 4P brochures incorrectly listed it as 14g and the manual listed EM at 13g. Correct spec is 18g, per Franc K. The specs for the Master Sig and Grand Cru come written inside the box lid and effective mass compatibility is given as a range. From my own and pictures I've seen, few if any of these cartridges show 18g withing that range. I don't know if you have the 4P and are considering the cartridge or vice versa. If you're looking to buy a Grand Cru you might consider asking for one suited for 18g eff. mass, otherwise it may require a trip to Holland for modification.
If you have the 9-inch 4P, its eff. mass is 13g which should already be compatible with most of the MS and GC. The 14-inch is rated at 19g.
Fwiw, I'm very happy with the 4P + MS sonics.