If I'm interested in the topic and have something to say, if the discussion is active, then I see no reason to count number of posts. I guess it was over 50 a day when I was passionate. But usually it is not what will happen every day. If one day I post tens of posts usually I feel myself tired of posting and make much less next. So there is no average posts amount, it depends on topics I read in exact day.

If there is a signature I can be a little more motivated, but I feel myself much more comfortable with campaigns without minimum quota as I don't like to feel that posting should be done.