I don't think too many expect Tahitian black pearls below 10mm.. no...
Adding to the question rather then the answer here: I am wondering if the recent popularity of rope lengths is not going to give a special place to the smaller black pearls.
After all, for the traditional larger sizes of 'Tahitian' pearl colors one would mostly see rope necklaces in ... commercial advertisements and hardly ever on the shelves of jewelers catering to financially daring clients.
If the rumors that larger blacks trickling down are right, their scarce presence at aspiration prices could only help a new form of presentation for the same pearl color... methinks. [
add lots and lots of salt: this is an economist who does not sell pearls and likes rope strands writing!]