remember though those guys have the ceramic ones - not the steel ones like the group A's found on australian delivered st185's
the Group A ones are mapped to 18 psi or so for their fuel delivery , though i think its more to do with intercooling cooling + head gasket then the turbo being too small.
The air to air definanlty is on the limit approachong 15psi for heat dispersion..
Still i think if youve fixed the gasket , you should be able to up the boost to factory limit and just get that bit more fuel in with the mod i can show you - and it will be fiine until you start looking at aftermarket ECU's and higher boost again.
believe me - for just street fun - i find 13-14psi plenty fun, though im insane - and mildly disturbed because i want more power ( but also have the engine to handle it ) ..
If your down my way i can show you whats been done to mine, oh and if you have some play money - DEFINANTLY invest in the aussie exhausts dump pipe .. youll notice a BIG difference right there