I think it's illustrative to look at the subwoofer world.
While it's not completely obvious to all people that if they're playing at -10dB they need to be able to handle 105dB peaks at listening position from at least 20Hz to 100Hz, it's something I think we have more experience with than the main speakers in home audio.
I wonder why that is? Is it because we've more often heard a system lacking low bass?
No one debates with Ricci at data-bass.com, "No, my six inch 50w sub that's part of my computer speakers is more than enough bass for me! Fills the room with LFE."
At his site, we see graphs of THD, with the low-end being limited by the the driver, and the upper-end is limited by the amp.
Generally, we see high Xmax drivers (30-50mm?) offering lower extension but requiring more watts, with less sensitivity, and they're often lacking in the mid-bass.
We see high sensitivity drivers not able to reach to the lower frequencies with as much SPL, but they do better higher up. 9-20mm Xmax.
A longer voice coil will be used with greater Xmax, but that means more weight in the moving mass of the driver, thus decreasing sensitivity.
Here's a list of drivers he's tested: http://www.data-bass.com/drivers
Ricci talks about shorting rings to smooth the inductance at the Xmax extremes, lowering distortion (I imagine just on peaks). He talks about the different venting/cooling designs (which would affect long-term power handling, thermal compression).
Aren't a lot of these subwoofer concepts applicable to the 70hz to 500hz of our main 3-7 speakers?
Anecdotedly, I see a lot of speakers that dig deeper have less sensitivity. I imagine box size and money can compensate; for instance using more exotic materials for cones and coils that are lighter. I read a good article last night about speaker design tradeoffs: http://www.trueaudio.com/st_trade.htm .... Like with Hoffman's Iron Law, the author treats Size, SPL, and Bass as shares of a pie. You can increase one of those attributes, like Bass (extension), but you have to give up SPL, or you'll need a bigger enclosure. You can't have deep extension, a little cabinet, and high output.