Keywee recently analyzed more than 230,000 organic posts from over 300 publishers and found evidence indicating that the amount of text in a Facebook post is in fact impacting how it is prioritized in News Feed, as well as its organic reach.
This article shows that the percentage of highest reach increases steadily as the number of words in a post increases from a small number of words to about 20 words. After 20 words, the ratio flattens out, no matter how many more words are used.