Well, I think larger posts counts would be good for ranks past 100. All ranks from 0-100 have 10 posts between ranks, so I'm thinking 20 between the newer ranks would be best, and 30 posts between ranks for after 300.
Don't worry, I'll think some up. I'll also be open to suggestions. Right now the ranks go right above people's avatars. The new forum system allows you to have a rank and custom text displayed at the same time.