Your better off with a forged engine, assuming the forged engine runs right.
Much stronger, standard engines are ok, but not much room for error with them it seems.
i have seen 300+ bhp b16a2"s on standard internals last years but maybe its down to lower compression of that engine. b18c6 i wouldn't run anymore than 8psi and with out a good map i can't seeing it lasting long.. save your money in the long run and forge it from the start is my advice
Boost/psi isn't really the concern, the power output produced at X psi is. 8 or 10psi on a 40 lbs/min turbo compared to same boost level on a 60 lbs/min turbo are going to produce very different levels of power.
Do it all once & do it right. Don't skimp trying to do it on the cheap avoiding things & finding how much you can squeeze out of standard parts which have already had a hard life. That's when things eventually go pear shaped. Better to do it right first time while it's all apart to ensure longevity.