I recently moved into a house with a roughly 15x28 foot room. Theater area takes up about half this, but obviously the sound has to contend with the whole room and the fact that it's in the LOWER level of a split level house. With carpet.
I assume you're talking about the Rythmik LV12R? I'm also of the opinion that it is likely to be better than the SW-311. You'll be paying more for the LV12R though since it is $599 and you have to add shipping.
You might also consider the SVS PB-1000 which is $499 (shipping included). Or the Hsu VTF-2 Mk4 at $559 (+$67 shipping).