How many times did an Oscar category feature five nominated actors or actresses who were past or future Oscar winners?

How many times did an Oscar category feature five nominated actors or actresses who were past or future Oscar winners?
There have never been five past winners in a category. But there were a few times with past and future winners nominated together:

1967 Best Actor- future winners include Warren Beatty, who won for direction
1968 Best Actress
1973 Best Actor- future winners include Robert Redford, who won for direction
1985 Best Actress
1990 Best Actress
2001 Best Actress & Best Supporting Actress
2002 Best Actor (four past winnners, and the fifth nominee won)
2006 Best Actress