go w/ one RE HC 12/15" ported in a 3 cube box.
I have one, and it friggin slams like a mofo. Louder than 2 12" type-R's, louder than a 15" L7 running on 1200 watts (my HC is only gettin 500), and i bet it will be louder than 2 10" L7's in that small of a box.
You will not be dissapointed.
:edit: i have also heard that a subsonic filter isn't necesarry for ported use, only if you're running a lot of power to the sub. The guy @ my local shop told me that most CD's are only rated to go down to 20hz, so you won't even have to worry about cutting out the frequencies if you were going to go w. a subsonic filter (i'm not totally sure about that tho).