On stock intercooler and stock injectors and stock fuel pump and stock cams ie totally stock engine, except exhaust and air filter I ran 1.2bar (about 18psi) and got 420bhp at crank. It also ran at 1.3 bar (about 19.5psi) and got 440bhp, but turned it back down for safety.
The turbos are stock size but with steel wheels, to allow higher boost.
This was on my R33 Le Mans that I have now sold..........running fine with new owner.
However, it is obviously less hot over here in England, so I can't say whether it would be safe to run this boost in 30 or 40degrees centigrade.
Guy