In that case Andy, it may be simplest to have 6 categories but to have fewer than 6 names eg.
1 pip, Newbie = 0-10 Posts
2 pips, Member = 11-20 Posts
3 pips, Member = 21-30 Posts
4 pips, Advanced Member = 31-40 Posts
5 pips, Advanced Member = 41-50 Posts
6 pips, Veteran Member = > 50 Posts