Im in the market for a header. Currently my setup on a b16:

Comptech icebox w/ intake
Mugen twinloop exhaust

I dont plan on adding aggressive cams (ie. Toda / Jun / Skunk).

My question is if I go with a JDM header (2.5" collector) and upgrade to a 2.5" cat will i make more power throughout the power band vs going with a USDM header (2" collector) and stock cat with my current modifications? Any input would be helpful.

-tell