[Gravy]

If you can, try cranking it up around the 18-19psi range. I'm not car god, but normally you go larger turbo for 2 main reasons, first off more boost. Which isn't making a huge difference in this case, but lets you boost more without spitting off really hot air. Or the second, to be more thermally efficient due to lack of a FMIC or SMIC for the most part.

The other thing you could look for with the hissing sound, do you have any leaks around the exauhst? That would cause similar problems, but would probably be more audibly noticeable.