I really like the first ranking, but maybe include police detective before high school detective, as well as famous detective and Holmes after the ranking detective. for instance:
0 posts and more => Novice
10 posts and more => Detective boy
50 posts and more => Police Detective
75 posts and more => High-school detective
100 posts and more => Detective
200 posts and more => Famous Detective
500 posts and more => Sherlock Holmes