I would think doing two 8's vs a single 8 would have quite a bit more potential. It will still be bad ass, two 8's can get pretty loud. If its going in a hatch back definitely. You just have to put them in the right box. Box shouldnt need to be very big at all. Not familiar with the car its going in tho.
I had two DD 1508's for a short while. I threw them in the shittiest ported box i threw together, no idea what size or what it was tuned to, but i used it in the rear "well area" of a third gen trans am, i only had a small amp, 250 rms to the PAIR and it was still pretty loud. I know that if i had gotten them in a decent enclosure and some power that shit would have been LOUD. Sadly i got rid of them for some 15's before i got to use them to their potential.