Definitely get the Acoustic. Math says it's the same weight as fire rated type X here in the states, which is what we generally use. Mass is your friend.On the inside of the theatre should I fit 5/8 PB or 5/8 Acoustic PB?
To be fitted to decoupled studs with OSB first layer - probably using Green Glue inbetween the layers.
I'm in the UK but the stated mass and price is as follows:
Standard 5/8 PB