The Rl-p18 is one of our front runners for HT bass, however, it requires 20+ft per sub. Kevin Haskins of Exodus audio, was contemplating building a new world class 18" sub for around 1k. If he does build one, it will be the the new flagship HT sub driver, once held by the LMS-5400 by TC-Sounds.
If you are limited to 11ft each. The SDX-15 will work perfectly. For amperage, you could hook four up to a Face Audio f1200-ts or QSC3602plx. You could also do a lot of other things when it comes to power. It all depends on what you want to do.
Do you have a picture of your room?