Well some catbacks are very mild the Invidia Q300 is similar in sound to your Tanabe axle back, so hard to quantify a number there.


I would say adding a RTP would increase your overall sound by about 30% and being resonated you should have very little to no rasp, similar to a Resonated High Flow cat w/ just a bit more volume. And you will get noticeable gains, but will have exhaust odor, so that's a trade off.

 

I have Berks HFC with Invidia Q300. It's subtle and deep, but screams appropriately at WOT. When I've driven people for work, they haven't mentioned it, unless it's from a cold start. It's pretty loud from a cold start, but even stock, these cars sound rough at a cold start. Driving around it's a bit louder than stock, and I get some cabin drone in the 18k-21k range, but I don't remember paying attention to that range while stock to know how much louder it is. I do think there's a noticeable power add in the mid to high rpm ranges

When I started making these purchases, the wife cautioned me that she liked how it sounded, and she wouldn't drive it if it was embarrassingly loud. After these mods (and an intake), she loves driving it, and says it's not loud unless you get aggressive with the throttle.

I think it's a good combination. You have noise and power when you want it, but if you have to creep into the neighborhood at 2am, you can do it without waking the neighbors.