How important is the efficiency of a speaker to you?

Not very important. 

The best speakers I have ever heard, and the best I have ever owned (not in the same set, I could not afford the best I've heard), have all not been very efficient.

My old Koss Model 1a full range electrostatic speakers were 87db. But the clarity, detail, attack/decay, soundstage and image they produced are better than pretty much any high efficiency speaker I've heard. 

 I can think of a few exceptions, like the Acapella Audio Arts Hyperion, with their plasma tweeter, and their built in amps for the woofer section. 

Not particularly important to me.

The amplifier takes time to make this power (i.e., slew rate). So the amp "slews" 3.16 times faster to reach the same volume level resulting in increased dynamics for the high efficiency speaker.

that's not how it works, that is not how slew rate factors into how an amplifier works. Slew rate is directly related to bandwidth, not how quickly it reaches peak power operating within it's specified bandwidth. 

 an amp operating withing it's specifications that is  producing  100 W RMS at a given frequency will reach peak power in  the same amount of time as a 1 W RMS amp will.

Example.... at 1000 Hz the period is .001 seconds. So starting at zero crossing  it reaches a peak  .00025 sec later , crosses zero in the opposite direction at .0005 sec, the opposite peak at .00075 sec, and back to zero at .001... no matter how much power it is producing..  If it didn't it would be distorting the signal. 

@danager 

Thanks for posting the link. 

@herman Would that be in Denver or NYC?

Efficiency is not the issue, unless you have a silly pea watt amp. What you like to listen to is the issue and speakers, being the most difficult of all components, are always a compromise. I'll only listen to Line source dipoles. They are usually not very efficient.