How much boost depends on what turbocharger as well. The stock turbo is going to make more torque and "hit" harder at lower RPM, which IMO is harder on the pistons ultimately than making steady power to redline. Running it above 22psi or so is going to generation higher IATs too, and that is definitely harder on the pistons. These are really strong motors as tested by companies like ZZP, but there's only to much real abuse it is going to take. If you want more power than the stock turbo can generate at an efficient boost, get a bigger turbo and run the same or slightly more boost, and have it professionally tuned. Delta LNF guys are running 400+whp daily, the weak link for them being the clutch and transmission. We seem to be blessed with a pretty strong drivetrain overall.
I should note that I'm not just making conversation lol, i'm putting my money where my mouth is. I'm trying to wrap up an EFR turbo install now with intentions to make high 300s/low 400s on a completely stock engine/drivetrain. I'm pretty confident with a little respect for the hardware that it will take it. It's not a race car, drag car or anything like that. It's a fun weekend car FWIW.
2008 BRAZEN GXP - 5M Loaded Tuned to 22 PSI with HPT, AEM water/methanol injection kit - 4gph, Hahn Racecraft Intercooler. Solo street race exhaust, Catless, LE5 Throttle body, ZFR 6758, custom CAI 307whp on dyno dynamics - stock turbo (21 psi) 463whp/454wtq EFR 6758 26-27 psi,100 octane - tuned by me
2006 SLY 2.4 Comfort and Power - TRADED 28-Aug-2008