Not all boost is created equal.
Boost is just a product of restriction. If you had two 3.8's, but one had ported heads with bigger valves, headers and such, and the other was otherwise stock, the engine with the work that improves flow would have less boost with the same size pulley/blower, BUT make more power.
It's not always as easy as "single digit boost is safe". You have to look at the size of the blower and projected power output. That's what I would be more concerned with, the max power on the stock valvetrain and rotating assembly.
You can have a smaller blower with 10 psi of boost make less power than a larger blower that only makes 5 psi of boost because of the larger volume of air it moves while working more efficiently (which means it won't produce as much heat which equates to more power).