Helen's portrayal sounds very young, girlish, and naive. She isn't bad though.
But Marin's portrayal is beautiful, mature, and in control. Your description of their performances couldn't be more on spot. I was trying to put into words how I felt about their Claras, but you said it the best.
Spork, I feel the same way. Donna Murphy's performance as Fosca is haunting in ways that no one has even been able to come near. I honestly can't even think of any actress that I would like to see in the role now. Laura Benanti said Fosca is one of her dream roles, if she were to be directed to give a performance like the one she is giving in GYPSY right now, then by all means, she should give it a go. She's good friends with Murphy so perhaps Murphy can give her a few tips. Then again when I think of roles I'd love to see Benanti play, it is Clara and not Fosca the one that comes to mind, but she could surprise us all.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"