It's not as far as you might think. Seriously, I've been averaging over 60 posts per day, without even trying. With a little effort, you could easily get 10k within 5~ months.
50 posts per page, then ctrl+f=today, and press enter to count them, is easiest way. Once you make the top 250 posters, you can just subtract your post count from that, since it updates daily now.