Michelle can handle pressure a lot better than Sasha, who doesn't handle it well at all. Sasha skated as well as she did at Worlds this year because she was totally overshadowed by Irina and knew she had no chance to win. But Torino is another thing entirely. Sasha wants to win very, very badly because then she can retire to a lucrative pro career.
I think Irina has the best chance of winning the OGM because she is the reigning World Champion, and if she can duplicate her Worlds performances she is in like Flynn. But that is a big if. She will be skating in Torino, not at home, and it was in Torino that she had her disastrous FS at Euros this year. I suspect the altitude at Torino may have been a problem for her, because her disease and the prednisone she takes to control it affect her lungs. Because of that, she really can't prepare ahead of time at altitude to acclimate herself without risking a worsening of her health.
About Kostner: yes, Kwan barely beat her in the SP and FS, but Kwan's jump content didn't compare to Kostner's and Kwan's programs were not CoP friendly, as Kostner's were. Kwan won on PCS, and because she didn't have good CoP programs, her PCS marks weren't anywhere as high as they would be with better choreography and transitions. Kostner still looks a tad gawky and her moves are rough and unfinished. Once Kwan adds more jump content, even slightly better spins, and better choreography, and she will be way ahead of Kostner no matter how many 3/3s Kostner throws in.