Newbee, thanks for pointing that out.
Regarding high efficiency speakers, I think that the point Minorl was making and that I was emphasizing would become clearer and less controversial if the reference was to highER efficiency speakers, as opposed to lowER efficiency speakers. For example, say 84 db/1w/1m vs. 92 db/1w/1m, those both being much more common choices than speakers having truly high efficiencies such as 100 db/1w/1m or more.
Using that example, and assuming that the two speakers have similar impedance curves, if the 92 db speaker requires say 50 watts to be able to produce the desired peak volume levels, the 84 db speaker will require 315 watts to do the same (assuming the speaker itself can comfortably handle that power level).
In general, it seems safe to assume that a 315 watt amplifier will usually cost dramatically more than a 50 watt amplifier, if they are both to provide the same level of quality. And the concerns that have been mentioned that are unique to "high" efficiency speakers (as opposed to "higher" efficiency speakers) would seem unlikely to be be particularly relevant at 92 db or thereabouts.
Regards,
-- Al