My ranking of the nominees so far...

1. Ingrid Bergman in Autumn Sonata
2. Elizabeth Taylor in Who's Afraid of Virginia Woolf?
3. Vivien Leigh in Gone with the Wind
   
4. Audrey Hepburn in The Nun's Story
5. Michelle Pfeiffer in The Fabulous Baker Boys
6. Natalie Portman in Black Swan
7. Sissy Spacek in Coal Miner's Daughter
8. Jane Fonda in They Shoot Horses, Don't They?
9. Judy Garland in A Star is Born
10. Julianne Moore in Far from Heaven
11. Glenda Jackson in A Touch of Class
12. Leslie Caron in The L-Shaped Room
13. Gena Rowlands in A Woman Under the Influence
14. Ellen Burstyn in Resurrection
15. Fernanda Montenegro in Central Station
16. Liza Minnelli in The Sterile Cuckoo
17. Ellen Burstyn in The Exorcist
18. Bette Davis in The Little Foxes
19. Diane Lane in Unfaithful
20. Joan Fontaine in Rebecca
21. Cate Blanchett in Elizabeth
22. Ellen Burstyn in Alice Doesn't Live Here Anymore
23. Meryl Streep in Julie & Julia
24. Kathy Bates in Misery
25. Katharine Hepburn in Suddenly, Last Summer
26. Maggie Smith in The Prime of Miss Jean Brodie
27. Patricia Neal in Hud
28. Michelle Williams in Blue Valentine
29. Meryl Streep in Postcards from the Edge
30. Simone Signoret in Room at the Top
31. Jane Wyman in Johnny Belinda
32. Carey Mulligan in An Education
33. Geraldine Page in Interiors
34. Gabourey Sidibe in Precious: Based On the Novel Push by Sapphire
35. Irene Dunne in Love Affair
36. Goldie Hawn in Private Benjamin
37. Jean Simmons in The Happy Ending
38. Pauline Collins in Shirley Valentine
39. Lynn Redgrave in Georgy Girl
40. Olivia de Havilland in Hold Back the Dawn
41. Barbara Stanwyck in Sorry, Wrong Number
42. Barbara Stanwyck in Ball of Fire
43. Mary Tyler Moore in Ordinary People
44. Rachel Roberts in This Sporting Life
45. Jill Clayburgh in An Unmarried Woman
46. Nicole Kidman in Rabbit Hole
47. Diahann Carroll in Claudine
48. Jessica Tandy in Driving Miss Daisy
49. Jessica Lange in Music Box
50. Jennifer Lawrence in Winter's Bone
51. Dorothy Dandridge in Carmen Jones
52. Bette Davis in Dark Victory
53. Valerie Perrine in Lenny
54. Anouk Aimée in A Man and A Woman
55. Jane Wyman in Magnificent Obsession
56. Doris Day in Pillow Talk
57. Ida Kaminska in The Shop on the Main Street
58. Greta Garbo in Ninotchka
59. Audrey Hepburn in Sabrina
60. Julia Roberts in Pretty Woman
61. Annette Bening in The Kids Are All Right
62. Faye Dunaway in Chinatown
63. Helen Mirren in The Last Station
64. Ingrid Bergman in Joan of Arc
65. Katharine Hepburn in The Philadelphia Story
66. Greer Garson in Blossoms in the Dust
67. Marsha Mason in Cinderella Liberty
68. Anjelica Huston in The Grifters
69. Joanne Woodward in Summer Wishes, Winter Dreams
70. Isabelle Adjani in Camille Claudel
71. Vanessa Redgrave in Morgan: A Suitable Case for Treatment
72. Greer Garson in Goodbye Mr. Chips
73. Barbra Streisand in The Way We Were
74. Ginger Rogers in Kitty Foyle: The Natural History of a Woman
75. Nicole Kidman in The Hours
76. Olivia de Havilland in The Snake Pit
77. Natalie Wood in Love with the Proper Stranger
78. Joanne Woodward in Mr. & Mrs. Bridge
79. Jane Fonda in Coming Home
80. Joan Fontaine in Suspicion
81. Geneviève Bujold in Anne of the Thousand Days
82. Grace Kelly in The Country Girl
83. Ellen Burstyn in Same Time, Next Year
84. Shirley MacLaine in Irma La Douce
85. Irene Dunne in I Remember Mama
86. Emily Watson in Hilary and Jackie
87. Elizabeth Taylor in Suddenly, Last Summer
88. Bette Davis in The Letter
89. Martha Scott in Our Town
90. Sandra Bullock in The Blind Side
91. Gwyneth Paltrow in Shakespeare in Love
92. Gena Rowlands in Gloria
93. Meryl Streep in One True Thing
94. Renée Zellweger in Chicago
95. Salma Hayek in Frida

As you see, I ranked Michelle's 4,5-rated performance above 5 performances. I felt I was too lenient so I took away 0,5 Meryls from the ladies below Katharine Hepburn in Suddenly, Last Summer.