I had that basic setup the first time I boosted a GS. I only had a narrow band. even @ 8psi and under, WOT still showed one or two of the orange led lighting up, the car pulled crazy hard. It wasn't until much later that I learned I was @ 14.0 AFR when I borrowed a wideband, and my egt's were reaching 1500. Luckily I never did any noticeable damage since those pulls were on winter nights (super cold air suppressing knock quite possibly)

At any rate, my point is try and borrow someones wideband for a couple pulls, play with the discs in your FMU (if it comes with multiple)or SFMU and get the AFR's low, and you'll be boostin fine for quite awhile.

I've seen more than a few guys in my region crack pistons during warm months hammering on this set up with no adjustments to fuel.

one last note, I run a narrow band meter beside my wideband and 11.0 AFR's will have the narrow band meter only lighting up the last 2 or 3 green LED's, in case you decide to wing it with the narrow band.