Possible Clues:

• Guinness Book descriptor
• Like 'Cleopatra,' among all Best Picture nominees
• Taking the most time
• Like Elizabeth II's reign, among British monarchs
• Tops in endurance
• Like the slimmest odds
• Like September of all months? Yes and no
• Maximally protracted
• Art desiring to be the greatest?
• Like the papacy of Pius IX, after St. Peter