The questions you asked have TOO many answers to them and it's like asking " How many stars in the sky?" i am sure no one knows ...anyways back to the topic, a stock ls can handle as much boost as it is prepared for if that makes any sense, i've seen a stock ls on 6 lbs and i've also seen a stock ls on 14 lbs, of course it has alot to do with the health of the motor, the age, the tune, the breaking-in process, what supporting mods you have, what turbo setup it is etc..as far as your t3/t4 question their isn't just one of them so you have to be more specific..you should REALLY just google these questions and read alot to learn, google is your friend