Well, it would obviously depend on what type of Cadillac you planned on decking out. If it is an old school eldo, than 2 12 600w + RMS would suffice with a sufficient amp with at least 100 watts more to push them. Be careful though, and tune the components to safely operate. Since the equipment would be placed in the trunk, find the best placement of the subs. Be sure to be creative and think different. If it's an Escalade (lucky son of a bit