A D series can handle 12lbs of boost if it's properly tuned, but you might want to get some forged internals. As for the T25, you can tweak the actuator and get it to open the wastgate between 6-10lbs of boost, or you could run an external wastegate. If you just want to be able to run 12lbs of boost safely, get some rods, pistons, a standalone, and get it tuned.