[Plums]

Not wanting to "start" anything on here, but can you provide us with proof that the smaller size is "producing better low end torque & a wider rev band"???

Your statement "may" be slightly true for engines running a Completely Stock PCM, but most people won't leave it like that for too long. Your "far better" statement is a bit of a stretch.....

In my experience (not opinion), for a well tuned stock LS1 (ie. a good MAFLess tune), 1 3/4 inch pipes provide the best overall performance. Even larger if you are running an aftermarket camshaft or you're chasing maximum effort unopened power levels.
If you're running a stroker or hefty head and cam package, 1 7/8 inch headers would be the smallest I would use...