Is there any advantage to lower efficiency speakers? 87 or below?

For a lower wattage tube amp you want both more efficient and easy load speakers for best results. For comparable bass extension those would need to be larger and probably more expensive as a result.

Very fundamental for top notch results  to match speakers to amps capable of driving them well and to the max.

In general the main reason to design a less efficient speaker is to enable more extended bass out of a smaller speaker. This has been the popular trend for the most part ever since higher power SS amps started to make their mark.