5 psi sounds safe for a stock set up!

I had a probe GT that I ran 6lbs of boost on with a stock setup for years and had no problem! The car ran a little lean at time, but it was not smart to boost in 5th gear!

On my Probe GT-ZE that was rated at 200 hp with high compression. I have friends that have ran 6lbs of boost on theres with no tune and made over 300hp.

Nevertheless, a good tune does wonders to the way the car run and power gains!