If you oprimize your Y-pipe you can retain the heat shields and you'll have perfect match to your pre-cat manifolds. You can also keep the 180 bend if desired.
The sho shop pipe is a little larger and will breathe better. Someone posted their results that had done both last week, but I cant remember who it was.
Optimized Y will get you about 85-90% of aftermarket Y performance with fewer fit issues, better heat shielding, and lower cost, (OK, I'm biased...)
