Higher sensitivity - more dynamic sound?

Frankly, any reasonably well designed and mated combination of speaker and amp can be sufficient.

Consider that most rock /pop recordings have a whopping dynamic range of maybe 10db. Classical will have the widest range, perhaps 30 db.

Good dynamics is not just about the range of capability.  It is more about whether, when the signal goes up, there is a corresponding increase in the output of the speaker (i.e., no compression).  This is less the case with low efficiency speakers because, more watts have to be delivered for any given volume level, and a bigger proportion of those watts are being dissipated as heat.  The problem with this heat is that heating of components increases resistance which reduces the flow of current/power.  In other words, there is not a proportional increase in driver output to the power being delivered to the speaker because of such heating.  This is thermal compression and it is a bigger issue with low efficiency drivers which, dissipate more of the power being sent through the driver as heat than is the case with high efficiency drivers.  

Ok, obviously I’m dog paddling in the deep end … but if the amplifier has a very large - let’s say infinite - current capability, so can maintain voltage to be applied as the speakers impedance changes with signal frequency changes …?

[I have a lot of reading to do]

@inscrutable wrote:

"if the amplifier has a very large - let’s say infinite - current capability, so can maintain voltage to be applied as the speakers impedance changes with signal frequency changes …?"

A constant-voltage amplifier will put out reduced wattage into a higher impedance.  That's just the way that type of amplifier behaves. 

However a constant-power amplifier will put out essentially the same wattage into the speaker's impedance even as it changes, at least within a realistic range of change. 

Most tube amplifiers have a constant-power characteristic, and therefore the system's dynamic contrast would be less sensitive to heat-induced changes in the drivers' impedances. 

Duke

Thanks Duke, that might explain why I really like tube amps feeding high efficiency speakers.  Most of the tube types I like don’t put out much power.  I like 45 and 2a3 in SET amps and 6L6 and KT 66 for push pull amps.  In my own amp that is currently in my system, I run 349s—two per channel for about 5 watts.