Well don't just stop this post. There is a better driver that out does Dayton 15. TC Sounds have very high excursion subs. If I'm correct that a 38.1 mm one way or 76.2 mm peak-to-peak might put you ahead by several marks. Daniel Marx have constructed a subwoofer that used TC Sounds 15 inch woofer that can go very low at high SPLs. It is a litte expensive but will win the contest no questions ask.
Info on Daniel Marx's 15 TC Sounds Subwoofer - http://216.150.71.139/audioinnovation/tcsounds.html A Store that sells TC Sound Drivers - http://www.audio-x-stream.com/