hi
i have the Apexi N1 in my 4gen, i think you can consider it loud, but the main question is if you removed the CAT, if so it will be pretty much louder, or if you take the secondary muffler , the exaust will be more free and it will be even louder.
some people i know removed the exaust and put a straight pipe from the 4.2.1 manifold , i dont know if the 5gen prelude will lose backpressure with that, but if not the results can be pretty nice, in performance thinking.
i have a friend who did that to a CTR2 and the car is pretty loose
but the noise is to cry for
i usually donīt use the silencer because i feel the car isnīt leeting "all go" at high RPM, but at lower RPMs the car is nicer to drive
hope it helps
XTension R