In a nutshell mate.the rs owners club put a figure of 0.63 psi as standard.I converted mine to a chipped ecu and before i put the ecu on i accidently fitted a -31 actuator (bought it off a mate who told me it was a standard actuator).The car flew and when I reached 17 psi the standard ecu shut the motor down.sounded like a double barrel shotgun and i shat meself.Looked in the mirror to see a fog bank which ive been told is unburnt fuel (thank god).I then ran it at 12 psi and it didnt repeat the shut down (thank fook).From that experience I would say you could get 12 psi but i am no expert.