Trust me, if you put a new turbo on the car without proper fuel management, the car will run like s***.
You *MUST* have a FMU or standalone to properly run a larger turbo on our cars.
For instance, my car back when I just had a boost controller on the stock T25 at 12psi walked OrangeMSP's T3/04e hybrid setup because of no proper management. Now the car SOUNDED like a beast but without something controlling everything, it just didn't have the umph it should have.
If that's not a good enough answer, talk to Spool if he's still up with helping us all out.