itll be pretty damm loud if properly powered/installed. its really easy to get a system loud in an rsx since its a hatch, but overkill is pretty subjective. most people are happy with a single sub setup in an rsx.
If the spl doesnt break the windows on your car, it's not overkill //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif