Six apparently equals sexy. When writers want to subconsciously make a character appealing they switch out the e for an i.
Tricia Helfer's portrayal of the Six line of cylons was universally considered on of the sexiest roles in sci-fi history.
#56 on The Greatest Female Villainssee more on Number Six
Voiced by Gina Gershon, Carmen Electra and Jenny McCarthy through 3 seasons of Tripping the Rift, Six is a play on Seven of Nine from Star Trek Voyager. see more on Six of Nine