I believe it's somewhere around 12 to 14 PSI, but I'm not positive.

I have not tried to boost it as I'm happy with the power as is for now. If I change my mind I'll probably go with a full Speed Innovations tuning job instead of messing with just the boost pressure.

An underdrive pulley set will increase the RPM on the supercharger and increase the boost pressure, but to realize the full potential, you will need to have your ECU tuned as well. Hence, going to SI for the job.