Viacin,
I, too, hated having to go through the members pages, one by one, to see the total members that have at least one post, until I found a shortcut. On the members list, there are 50 per page. Go to the 2nd page and take a look at the end of the URL. It says 50. Go to the 3rd page and it says 100. 4th page - 150. On the first page, there is no number. Therefore, to advance to the 30th page, for example, start at the 2nd page and replace the 50, on the URL, with (30 -1) X 50, or 1450 and hit Enter. You will be on the 30th page. This works no matter how you sort them.
This works the same on a member's posts, except the number of posts per page is 15. Today, for a certain reason, I wanted to go to the 31st page of my posts. I went to the 2nd page and replaced the 15, at the end of the URL, with (31 -1) X 15, or 450.
I just discovered this today. Check the end of the URLs and you will find it works for other things, also.
Actually, you only have to go to the 18th page of Members descending to find how many have made at least one post - 890 people - 17.7% of the total members.