Tubes Asylum: efficiency and speakers for a low powered amplifier by asterisk

I know this possibly could have been put in the 'speakers' section however, I belive this to be related speakers for lower powered valve amplifiers more so than speakers in general.

I currently have a single ended KT88 amplifier capable of around 8-10wpc in UL (a bit less for triode mode) and currently have it hooked up to a pair of BOSE 301 (...ok stop laughing now) with an approximate efficiency of 89db per watt per metre. I find that the volume I can achieve from this set up is ample (approx 98-99dB) , in fact, near deafening when at full throttle (not literally but very uncomfortable).

Even if I were to use speakers which were rated at 86dB/W/m the volume difference would only be 3db which is considered only just noticable.

I don't understand why I keep hearing advice recommending that people with 50wpc amps (even higher) should stick with speakers that have efficiencies of greater that 88dB/W/m.

Is there something I am missing here? Is there some other reason that an amplifier should be able to drive speakers up to SPL's of 107-109dB? Is there another factor such as dynamic range, transient peaks or control over the driver that I don't know about? Or is the efficiency purely related to the maximum achievable volume?