What gen and model do you have? . I'm guessing 2nd gen since you're talkin' Supra 550's. Just adding the injectors and uping the boost will only make you run pig rich without any gains. The stock turbo will never out run the stock fuel system. Even @16psi.
Alot depends on the condition of your engine. if you up the boost to 15psi and your engine is in good condition-maybe 200rwhp. and thats only a guess..
But if you do up the boost, you will feel the difference!