What MAP sensor are you using? I ask because the stock MAP sensor maxes out around 22 or 23 psi.
I have an ATP 3076, with IWG, Hallman MBC, and an AEM 3.5-bar MAP sensor, and I have been running 22psi for months. I had it tuned for 25psi for a little while, and I didn't have any trouble getting there.
I get about the same boost taper that you do - boost drops about 1.5psi between 4000 RPM and 7000 RPM. I've been told that an EWG would fix that, but it doesn't really bother me.
I am running the IWG actuator that came with the turbo. If I remember right, I get 12psi with the MBC turned all the way out (min boost). But it's been a long time since I actually checked.