Either way, Pete hit the nail on the head with his comment. Specific applications needs specific solutions.

As my particular application ATM is about getting as much torque as I safely can from a sub-300HP set-up on an MY03 WRX (balancing that desire with other considerations though - e.g. the *noise* from a CAI), the question around 2.5" diff-backs interests me.

Tuna... I appreciate your input here on this topic too. You sound well-qualified about these sorts of things!