30psi. :S Not on pump fuel or without water injection.
Boost is a restriction to airflow. You need to get the motor breathing well. If you cant get it out the only way to get more in is by pushing up the boost.
The GT35r is good for up to around 400rwkw.
If the build is well thought out. Around 20psi on pump and no need for WI. If you simply bolt it on with a pair of cams don't expect to push much past 330rwkw. Cams, plenum, exh. manifold are all needed.