Most Efficient Header and Exhaust Design

[rh77]

OK, so there's an age-old debate on which header and exhaust makes the most horsepower, but what about fuel economy? I have an exhaust leak and all but the Cat must go. 80/20 Highway/City driving. What is the opinion:

* For the Integra, should I go for the 4-into-1 header, or the 4-into-2-into-1 header?

*Backpressure: leave the stock exhaust diameter
or go larger (or smaller, for that matter).

*The RS-R Ex-Mod may be the muffler of choice (instead of a stock replacement) for sound preference and free-flow.

The CO is getting to me at stops, so everything must go (but the Cat seems to be doing the job for now).

I'm willing to take a sacrifice in power for better economy.

RH77