Are you talking about the Garrett Ball bearing GTP38R turbo? Besides the poweroutput the main thing is how much better will his powerband be? With ball bearing cartridge won't that thing spool up a lot faster then the laggy stock turbo? I think that turbo supports almost 500HP?
By the way I was reading the ATS aurora 2000 hits full boost like 4-5 seconds faster then stock. But I dont think they make it for the 99-03