Man i wish i had all this info when i was looking for a turbo, for a street car theres no need to go for anything past a highflow or a direct fit GTRS or something T25/28 based, like everyone else said response is what you want for a street car, why would you want a lag monster?
You cant go past a direct bolt on for $$ and for performance... standard manifold is fine just look at setups and results from all the other forum members, and if you don't plan on opening up the motor i wouldn't go for a GT30 besides as soon as its spotted by the cops/epa your in for big $$... its just not worth it if its just a street car. If you go track/drift/drag car then i'd understand but its only a st car...
Seriously, listen to the people with experience (i wish i did) save yourself a motor and save yourself some $$ and headf**ks.