How to Delete Stupidly Long Usernames?

Hi,

I have an article directory using the wordpress platform, since it is set up so anybody can register, I obviously have some trouble with spammers. They don’t cause huge problems but some register their usernames as whole paragraphs. I have 40,000 users that I need to sort through.

I am desperate for a mysql query I can use to find user names that are excessively long. A query that searches wp_users and finds user_nicename that are over X amount of characters long.

Is this possible? If so, could someone do me a huge favor and give me an example of a mysql query to perform to achieve this?

Thanks a million.