Frequency Response

I will go out on a limb and just tell you that 20Hz-20KHz reasonably linear i.e. +/- 3Dbn is fairly standard fora large floor stander. My Focals actually don't extend done to 20 cycles but stops around 27 Hz. I don't miss it but some people like the vibration that a subwoofer typically provides. I find it ludicrous that people can't just give you an answer. It should be noted that linearity is very important but you didn't ask for that information.

I guess it should be noted that measurements are made in "anechoic" chambers which are not like most listening spaces. (I would say any but someone will find an objection).
Also that human hearing is supposedly limited to at best 20Hz to 20KHz. As you age you lose some of the upper frequency hearing ability. Many argue that higher frequency overtones etc. can still be percieved in some way, making the extended upper frequency response from the speaker meaningful. I don't know if it does or doesn't.
What you will find is that most speakers don't give you the lowest frequencies as I and several others have noted.
Finally the specs really don't matter all that much. If I told you the horsepower of a car, absent of anything else, especially test driving it what good is it? You understand my point I'm sure. Go out and listen if you can is my advice and don't get to caught up in the specs for anechoic chamber responses. If I had one spec to focus on it would be sensativity which is important because it tells you what kind of amp you'll need to drive them.