Driver efficiency vs. overall speaker efficiency

I haven't grasped your reasoning behind the extra 10db. Anyways, speakers sporting at least one driver with a 87,5db rating would probably be < 87,5 overall.
Unless you're thinking of s/thing else? Cheers

In many cases, when you load a speaker into a proper cabinet, it can increase the efficiency level by about 1-2db.

To get more efficiency than that, you would need to go to a horn loading system which can increase the efficiency of the system.

You can't measure the efficiency of a bare driver. It needs to be in some sort of test enclosure. The test enclosure is not the same as the final system enclosure, and may yield a lower efficiency measurement. This is not a problem if your objective is just to compare different drivers (all tested in the same box).

Twl is correct.

Though, one should question the heck out of companies who use drivers of 88 db/2.83 V sensitivity and then claim the speakers are 94 db/2.83 V sensitive. I know of one famous one that plays this game egregiously.