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.
Efficency- Low vs. Hi?
Im trying to figure out the point in speakers with very low efficency, for example my speakers which are 4ohm and 86db. As far as im concerned they have no benefit besides being able to spend much more on an amp to get them to move. Right now they sound shut in, boring and thin with my Cambrdige Integrated amp, which is rated at 65 watts 4 0hm. I do not really have the budget to spend hundreds MORE on a power amp just to get these speakers to sound as good as a high efficent design on a lower powered amp, such as my current cambridge. So what are the benefits to having power hungry speakers? Why should i have to spend tons of money just because my speakers are designed with poor efficency?