2 inch pipe vs 2 1/4 inch pipe

This is nonsense. Automotive engines DO NOT gain torque when the exhaust is sized down.

IF YOU are working with OPEN tuned headers, you can tune the collectors for more/ less torque and HP, but once you add the restriction of a "full" exhaust system, you pretty much are better off to make it as large as possible.

I doubt very much that any full -- to -- the -- bumper systems are "tuned" to promote much scavaging, and once somebody changes the mufflers, that's all changed.