I honestly love my non res set up, my buddy has the 18"s and I think it's kinda quite when in the lower rpms and I haven't heard a 12". Do you plan on running HFC or test pipes?
I do want a noticeable growl at lower rpms (driving around town), and it seems like the 18"s might be a little too quiet unless I step on it. I have CF 18"s on order but thinking about changing to the CF 12"s. Knowing that non-res is the loudest set up possible, are you having issues with listening to radio or conversations in the cabin?