vinnieg: i'd say 1 bar or 14.7psi is semi safe.
To be honest, on the stock exhaust, stock fuelling system etc, i would run stock.
Once you open your exhaust up to say a 3" your boost will rise to about 12psi.
Also with B4s they are sequential turbs? so the first turb to kick in is probably where the reading si taken? max boost on either turbo is about 17psi since they are steel wheeled. But small turbos.
Also depends on what fuel, run it on 98 to minimise detonation.
Best to take it to a tuner, where are you located? In Wellington, Shred Performance do good deals. Chch i think still has EFI Tuners?
Also check out clubsub and subzero if they still exist for some good reading
so it compesates adding more petrol when u add more boost? im guesn id have to get the ecu changed aswell then.