The Avionixx 1100D has better features (remote gain, better xover, subsonic filter) for the same price. That would be my choice if you're wanting to run that much power.
http://www.edesignaudio.com/ep/ampspec/tsunamispec.htm
A pair of Shivas would be both loud and clear, but they would take up quite a bit of space. I would probably run a Brahma 12", Stryke HE15 (if they still make them), Stereo Integrity Magnum, or JL W7. Remember that doubling cone area only gains 3db. I've never felt it worth paying 2x as much money on subs for the marginal gain.
And please tell me you have upgraded your stock speakers...