What am I being told that a speaker with 92 DB is better than a speaker with 87db?
Not necessarily better, jut easier to drive to a volume level.
For example, a 87 db (at 1 watt, 1 meter) speaker can reach the volume you want with a 200 watt amp.
If you have a 90 db ( at 1 watt, 1 meter) speaker, it should reach that same volume level you want, needing only 100 (half) watts.
If you have a 93 db ( at 1 watt, 1 meter) speaker, it should
only need 50 watts to reach that same volume level again.
So, if these speakers were 100% identical in every way, including sound, looks, size, etc, I guess you could say the one with the higher rating can be better, since it needs less power, if everything else is equal. The all else being equal, usually doesn't happen. This just helps you find a speaker that can play louder for a given amount of power.
This Wikipedia link may help more. [http://en.wikipedia.org/wiki/Loudspeaker#Efficiency_vs._sensitivity]