So, i know that the stock turbo has a maximum boost of 14-15 psi, pumping about out 227hp.

If one were to keep the same turbo setup, what is the max boost allowable (safe) by use of a boost controller? And the approximate corresponding HP?

Where did you get this 14-15psi stuff from?

I thought it was 13.5 stock

most people set it at 15.5psi for best results

14.5 is stock psi i had thought?

Everyone is getting different boost. Some people get 13.5, some are getting 15psi. I got spiking to 15.5 and it would settle on 14.8. Most people agree that the stock turbo runs out of steam around 16-17psi. I have my mbc set to 16.5psi. I see less spiking than with my fbc. Do a search and you'll see that some people think it's bad to run anything higher than15-15.5psi. Read their posts, then learn how to read your boost guage to find out what is dangerous and what's not, then decide if you want to go run higher boost.
Good Luck,
Marcel

It really depends on your location. People at sea level can see higher boosts. I have seen upwards of 14.7 psi (.1MPa) on cold, dry days, and I'm at 300ft, I think (whatever Dallas is). Naturally, people in higher elevations can't see as high a number, so your mileage may vary when it comes to boost.