Bro, myself is a 4g13p aeroback iswara owner. So, if u would like to gain on pick up, it's simple.

1.EXTRACTOR 421
2.THROW AWAY ORIGINAL MIDBOX , REPLACE IT WITH A NEW BULLET/MIDBOX(2" will do)
3.CHANGE YOUR STOCK SFLOW MUFFLER TO STRAIGHT FLOW,(I RECOMMEND MONZA BIG SIZE..SOUNDS LOW BASS AND QUIET IF U R USING THE MIDBOX I RECOMMEND)
4.1.7" FULL PIPING/ SEMI PIPING...BOTH GIVES U DIFFERENT FEELING WHEN DRIVING..

*FC is depends on ur right foot..as long as your setup is correct and no wrong way of modding, it should give u better FC becoz restriction is less and negative backpressure for your manual tranny increases fuel efficiency...