honestly mate, at your level of modification i would not waste money on headers. I would only worry about changing headers if your looking for BIG power. a bigger intercooler, more boost and tune would be a much bigger power increase than headers. Im pretty sure others will agree. There are better mods that are more noticeable at the seat of the pants, which at the end of the day is the most important thing.
Dont forget things like brakes and suspension. Cars got to corner aswel.

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STi Ver 6 | 2.1L Stroker | 418whp | 11.5 @ 199kph |

Not fast enough dammit!