What ever you want your max boost to be, your boost curve must be linear is no more than 15psi @ 3000rpm otherwise the ecu will cut the fuel and go into limp mode So if you want to have higher than 15-16psi boost be aware that your engine will hAve to make more rpm to see your max boost.
The norm is 15-16psi which is considered safe.
There is alot of reading in the Dawes and needle valve threads just waiting to be read that explains safe boost levels.
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.
Most with the Dawes/ valve fitted are set around the 16-18psi.
Sitting on 120ks mine is 14-15psi and 340c. Max temp I have had is up bulli Pass sitting on 110 5th gear went to 580c.
Top speed was 133klm.