Specs are over-rated. For instance, I auditioned a ML Dynamo sub that claims 25hz @-3db. The spec itself is not terribly horrible, but the extension was incredibly lacking, even though it tries admirably for being so tiny. For my ears, even bookshelves that claim such-and-such spec still always give it up in the midbass, as far as I what I have heard. How can that be if they claim such-and-such spec? I do not have an answer, but its what my ears tell me.
Anyways, I think everyone will agree that the need to step up in the line is very dependent on the room size.