The turbomaster pages list two pressures for the turbo wastegate used on the 2.3
http://www.turbomaster.info/despieces_garrett/466272-0002.php

On my 4BD1T the wastegate originally needed 20psi to open it (20 is only just acheivable). I've moderated this to 15psi and the engine runs much better with less backpressure.

IMO trying to run more than 12psi without an intercooler is futile. The extra heat in the air and it's resulting expansion mitigates the extra boost and leaves you with only a few percent extra air molecules for a lot of extra restriction on the engine exhaust.