To 'push' 4000 watts, that amplifier will be drawing somewhere between 275 and 350 amps. For a daily system doing anything but a short burp, you are NOT getting that much power from your amp. Your voltage will simply drop too much. That's not even including the rest of your system. If you think you are getting 4kw or more, you are kidding yourself.
In all likelyhood, the guy with the eight 12's will be louder. If he's not, something is wrong with his setup. He has you out-displaced by a good amount.