What year M103 motor do you have? Some of them are 9.2 to 1 and 12 psi is no problem. Just need to retard the timing under boost. 6-8 psi should be no problem. I would install a Bosch blow off valve from a Volvo or Ford. They are fairly cheap. This will help save the Turbo bearings from blade braking. (That is when you let go the accelerator and the throttle body closes off and the air pressure has no where to go so it causes the turbine wheels to almost stop suddenly. hence Blade Braking and yes in some high boost applications the blades can break off)

I would not worry too much about the bottom end of your motor it is very strong. We have run 380HP on the stock motor with no problems. (compression 8.5:1, 16 psi, Water Intercooled)

ADAM - Good deal on the turbo! but that is one from a Starion non intercooled. but it will be fine.