ECP90

Hello, I've pulled down my old ceiling, due to 100 years of cracking and fixing (it was old horse hair stuff). I'm looking to board my living room ceiling with my bedroom above it with 12.5mm plasterboard and to insulate it using rockwool for the soundproof mostly. Will 40mm screws be alright or should I use 50mm to take the extra weight of the insulation. Thanks in advance.