Nate,
There was a guy that did ITB's on his DSP GSR from NJ in the '01-'02 timeframe, but his name escapes me. I think he did dyno time with Chris Shenfield, so you may want to ping Chris.
As I remember, he did not make much, if any, more power than Mike Neary did with a larger TB and stock intake manifold. However, I thought I remember that the condition of his engine was questionable vs the condition of Mike's. You might talk to Neary as well. This is from my questionable memory so, take it as you will. 
Eric