For paragraphs I've always tended to try to stay away from too much in one paragraph for being too bulky. Sometimes a paragraph is meant to end where it's at. So I think personally, a range of sentences should be best. For example, a paragraph has to have a minimum of three sentences to be considered a proper english paragraph. But where dialogue is concerned, sometimes it could be as short as one sentence or even two. 10 is a little on the long side, especially if you've got longer sentences strung together with commas. Perhaps it would be better to say an average of 5-8 sentences per paragraph?