Thank you everyone for adding to the discussion. I suppose it does vary a lot by what background your writing has. Journalism, for one, use the 1-10 cutoff because on a magazine page or newspaper article you are often limited by how many words can fit in the space allotted. While I'm sure that other writers who were, at one point in history, paid by the word preferred to write them out and put the cutoff much higher. Most of us don't really have either when we write, so what we choose to do with numbers is a stylistic decision entirely up to the author. I love that.