3 months, or a year would work as well. I just think all other sports and hobbies establish their leaderboard through points established over about 6 months or a year. Soccer, rugby F1, boxing, tennis. You go up the leaderboard depending on your latest points, and you disappear off the leaderboard if you're inactive.
I enjoy the 250 top user list, it's great. But why not introduce a leaderboard which reflects the current consistent leader over some months or a year.