MkIII Maxx Boost

Just after a little advice on the safe boost level for a 7m-gte with a Metal head gasket. I have a T04 on it and just woundering what the standard internals can take.

7M's should be able to handle around 16-18psi on stock internals without too much hassle - depending on how old the engine is - how many k's its done - etc etc