Hey Rikki, I have the 18'' res. Honestly, I would stick with your HFC if you're concerned about noise. The RTPs definitely add a hiss when letting off the accelerator, but I can't complain about the bump in power.
If you're looking for a quieter setup... try posting a trade on the parts for sale section. Believe it or not, there are people with the FI CBE that are looking for a louder setup and may be willing to trade mid pipes with you.

hi Tony, what is ur cbe set up? Is it 12" res or 18" res? Did u join our BAZ page? I hope to hear from u soon. I kinda need ur experience bcause I am still deciding whelther getting the res tespipe or not. I currently have HFC and non res FI cbe and its so loud especially at low RPM (>3000rpm)... hit me up on fb.
Rikki phan

Rikki! Sorry for the late response man, haven't been on here in a couple of weeks.
I have Fast Intentions resonated test pipes and the cat back exhaust with Uprev tune. 313 WHP, 257 lb-ft. See you next meet!

hey Zdar. I believe u live in san jose. I live in san jose either. I am jst wondering which bolts on do u have on ur z?I currently have stillen gen 3, FI cbe, hcf. Iam gonna get a tune soon thats why I am sort of need some info and experience about it. hope u can share ur experience. We actually have a big meet going on at 1:00pm tmr. hit me up if u re around.
206-466-7504