I have looked in the service manual and can not find any indication of a "safe or max boost".
Throw the vehicle on a dyno, up the boost gradually until there is no further improvement (around 20psi would be about it) or until it starts to go into limp mode, ensuring of course you keep an eye on EGTs, that should indicate the MAX boost for your ride/set up, then settle on a safe limit of say 2-3 psi lower.