Efficency- Low vs. Hi?

Your low efficiency speakers will play deeper in the bass region than a high efficiency speaker with the same box size. There's a tradeoff between bass extension, high efficiency, and small box size. You can have any two of the three, but not all three.

If you're comfortable with larger boxes, then you can expect deeper bass, higher efficiency, or some combination of both.

This is a great question and not simple to answer. One benefit to lower eff. is in tone. It is easier to come up with a warm full tone than say with super high eff. horns which need tubes to make up for their bright ballance. There is allways a system synergy going on with any combination. None is better,none is wrong or wright. Its all a trade off. I have the exact same speaker numbers and amp power that you have and have no problem at all with volume or openness. The problem in your setup, is the current ability of the amp. Not the power output! the speakers present a load your amp is not happy with-just and only a system missmatch. A 50 watt BEL mk5 would blow your speakers apart without breaking a sweat because it has huge current. The power rating is way over rated because it never takes into account the load in real world use. Also just try a high power amp with super eff. speakers and be ready to race out of the room. Those low power amps are just a better match. System matching is by far and away the most important part of the entire chain. Low price equipment well matched will beat super super expensive equipment that is not well matched.

Interesting question that's been asked before. SEARCH for more info.

There's no particular benefit to low sensitivity in moving-coil speakers that I know of, and low sensitivity is never a design GOAL, AFAIK. A designer may fall in love with a particular midrange driver that happens to be low in sensitivity; everything else has to be built around it. A designer sets as a goal high power-handling capability; that requires higher-order crossovers, which as a negative affect consume more energy than single-order crossovers.

There are lots of reasons speakers are low in sensitivity.

I must ask--why did you buy those unnamed speakers?
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Isnt it great to have Duke posting and helping on this site! I always look forward to his responses!

Not to pick on you Dave, but I wouldn't consider the Cambridge being low powered at 65 watts. My amp delivers 2 x 25 watts......