The SoundLab ESL's are considered by some to be one of the best sounding line of loudspeakers available. They are also notoriously insensitive, and a very demanding load for a power amplifier They are also extremely transparent, and about as good at reproducing instrumental and vocal timbres as any speaker I have heard..
Then there is the Altec Voice-Of-The-Theater loudspeaker (A7), a very sensitive and easy-to-drive speaker. I lived with a pair for six months, and consider it to be as colored a loudspeaker as I have ever heard. Intolerably, comically colored. It's akin to a video monitor with it's color temperature WAY off, and its contrast control turned to max. Nasty, ugly sound, like chewing foil.
If you compare the two, and prefer the A7 because it is more sensitive/easier to drive than is a SoundLab, we'll have to agree to disagree. That's like preferring a smaller house to a larger one because it's cheaper to heat and cool.
Of course, it all depends on one's priorities in reproduced music. If dynamics is your No.1, high efficiency is for you. I myself am not willing to give up transparency and/or natural timbre reproduction to get dynamics. Are dynamics and transparency/lack-of-coloration mutually exclusive? I haven't heard everything (including the Tektons), but from what I have, I find the two inextricably related.
