I was just looking at the directory and some of the sites have a huge number of questions. But looking at the sites, most of the questions seem to be unanswered. Game Shampoo for example have over 70,000 "questions" but there are 2,907 pages of unanswered questions! That's at least 58,000 questions without an answer.
Whereas Frageee has 20,000 questions but only 120 unanswered questions. Maybe the sites could be ordered by the total number of answered questions instead? You can still show the total number of questions.