~12psi for the stock spring, they run an ECU controlled wastegate actuator from factory to get their stock boost and then dumps back to ~12 as a safety.
car made 245kw @ 25psi on 98, any more timing and it starts to knock lightly in 4th.
maybe needs a little more boost, but cant do only a little more with the current boost controllers minimum duty, but seems to good enough for now.