I ran my car stock then put on a stromung dual tip(without midpipe). I also have an air/fuel meter. With the stromung dual tip the noise was INSIDE the "cabin" (where you sit, droneing in your ears). The air/fuel meter has a bargraph on it and with the stromung dual tip it read "one" bar leaner than without the stromung dual tip. It was still one bar on the rich side. Power came on stronger at 4000 RPMS.
I then finally bought a stromung midpipe. installed it with the stromung dual tip. The noise is now comming out the back of the car, not droneing in your ears, much more tolerable. The air/fuel meter is now running one bar less (14.7:1) perfect! The car pulls harder up till 4000 and from there its the same as before. The power curve is now very linear, much better.
The bottom line is "Yes its worth it, If I had to do it again I would buy the same thing!"
I also have an ISR K/N air intake
Its on a 2000 RS 2door
The air/fuel meter has 10 bars on its graph, 5 lite is 14.7:1 Its made by K/N.