if you take nothing else away from this thread, take this

it makes ZERO difference what exhaust you put on the car. Either a Y pipe + "single type" exhaust (NISMO, Fujitsubo,JIC DE Type 2, JIC DE Type 1, etc) or a true dual (Borla, Injen, HKS). The only measurable change between any of this will be

1. how much you spend
2. what it looks like
3. what it sounds like

Beyond that, on an NA car, they all produce gains that are nearly identical (that is to say, not much at all till you do the plenum, cats and/or test pipes)

 

That's what I thought too. I have the Injen SES1985C dual cat-back and here is the dyno test.
16hp gain