psi is pressure. it's not a measurement of air flow. that's cfm.
a larger turbo,a ssuming it's in it's efficiency range, will make more cfm at X psi than a smaller turbo.
psi should NEVER be a goal, but rather the number required to reach said goal.
It depends on your motor, the build, the tuning, the type of driving you want to do, the effeceny range of the turbo, etc etc to size one correctly.