Speaker sensitivity?

To a large extent there is no direct relationship. Some of the better speakers have low sensitivity and therefore require high power, high current amplifiers. When properly driven these speakers sound super. OTOH, many high sensitivity speakers have low mass driver elements. Less mass, less inertia -- the speaker cone should be able to respond more quickly to the music signal. Speakers designed along this principal can also sound super. My personal opinion is that it should be cheaper to design a high sensitivity speaker than a high powered amplifier. Regardless, either path works.

Some of the best speakers on the planet are very high sensativity; such as the Wilson WAMM, Cello's biggest, and the B&W800's, to mention a few. When these are couples with super powerful great amps, the sound is amazing.
Remember, doubling power increases volume by only 3 db. So, to match say a 600 watt amp into a 93db/watt speaker senstivity, one will need 2400 watts for an 87db/watt speaker.
Just remember that if you choose a low sensative speaker.

Thanks for your answers; this is one question i have never seen asked. Thanks!!!!!