Boost is currently set at 0.8-0.9 bar. The pistons have a potential of reliably sustaining 1.5 bar, though I suggest you upgrade the conrods for that appplication...
As for the N/A engine - turbocharged conversion, I have thoroughly discussed with my mechanic (A reliable and very knowledgeable one, countless engines rebuild by him, specialty in Subarus) and he has confirmed that other than the additional oil squirters and different pistons, the 93P block is pretty much the same as the 93T in the same way that the 63 NA is similar to the 63T (VR4-Evo3 Gen). The GZE pistons give a lower compression ratio than a standard GSR as well, making the engine very safe for boosting. The conrods however wont be reliable at 1.2 bar and above with a TD05 or equivalent or better turbo.