I expect the fluff hasn't changed and that there're about a thousand space marine chapters. Of course, GW can only really focus on a few, because the awesomeness of a chapter can be diluted.
So, mean or median, I don't care. If you were to estimate the strength of the average SM chapter, which fluffed-out chapter do you think best represents their capabilities? I mean, it's unlikely there're 700+ unnamed chapters all proportionate to the Ultramarines or Space Wolves.