The sensitivity of the speaker will only tell you how loud it will sound with 1 watt of power at 1 meter distance. The "load" of the speaker, or how hard it is to drive will be dictated by its impedance dips, or lack of it for that matter.
A flat impedence speaker will actually be easier to drive than one that drops to ridiculous levels, even if that speaker is rated with a higher sensitivity.
This is were Amp + speaker matching comes into play.
For starters, some speakers tend to dip to 2 ohms at a certain frequency (B&w towers i think ), if the amp is not suited for such extremes - chances are you will bust your amp.
The graphs will help you match the speakers and the amps, as for the preferred SQ - that's an all different matter.
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