As a Velodyne dealer, I'm going to recommend dual DD18's for that size of room as I have the most experience using these subs in that size of room. To be honest, I don't think a single sub of any caliber will get you what you want.
Other options are dual JL Fathoms or Triad Platinum Powersubs. On a budget, the HSU subs are tough to beat.
Other options are dual JL Fathoms or Triad Platinum Powersubs. On a budget, the HSU subs are tough to beat.