I think it would be great if you would set a UTC deadline each week whereupon you count all the posts before it in the previous week and all after in the next week.  That would help your posters follow along with respect to their own post count.  For example, I don't know if you've already started counting my posts so its hard to tell whether my posts today will be counted as last week or as next week.  Do you know what I mean by this?