on a standard bottom end,
if you want nay sort of reliability and not have to worry every time you hear a funny noise, 17-18psi personnly i think is a sensible figure.

probly nearing the turbos limits then (around 20-21 psi i recon)

at 17-18 psi with a good intercooler, little bit of a head polish and a mild cam, a very solid 200bhp is possible, thing some one got 220bhp at this boost on a similar spec,

nick from peformance ford got 250 bhp at 15psi, but with a roller bearing turbo, tubular manifold and a stage three ported head.

just my 2 pence though lol