3.5" to 3.33" Novi2K Pulley Swap..How much Boost?

Anyone know how much of a boost increase with this switch? There seems to be a lot more info about the N2K for 5.0s than 4.6s. I'm currently running the 6.87" lower and 3.5" upper and my motor is stock except for a catless H-pipe and novi/intercooler setup. The car made 415whp/362wtq on the dyno @ 9psi. My intention is to retard WOT timing a few degrees for safety and get the boost to about 12-13psi with the power pipe. I don't intend on spinning the motor to redline either.
thx