The Type X is definitely one of the best SQ subs I've owned/heard. It is not particularly efficient and won't be the best bet for SPL. But its loooowwww end extension and enthusiastic and accurate reproduction of those ranges, is very hard to beat.
Keep in mind that they just barely get out of bed and haven't had their coffee yet, until you feed them a piping hot cup of 1000 Watts. They need the current to move around the big ol' motor/piston with authority.
Also, sealed is the way to go. They'll work fine in a proper ported enclosure but their T/S params indicate that they are particularly at home in a sealed cabinet.
Yep, RL-P is also an excellent choice. Probably the slightly more accurate (SQ) of the two, and definitely easier to make louder than the Type X, plus only needs about half the power, but doesn't quite have the extreme low-end of the Type-X, as previously mentioned by Spkrman. If you're wanting a 10", RL-P's are out, since they're available in 12" and 15".
I'd take a Type X over an MTX 9500 in a hurry.