For what it's worth, for me Redgrave was by FAR the weakest performance of the leads when I saw it. I adore her and have seen her a couple times and she was great, but this wasn't her thing, or maybe she had an off night... but I've heard similar things from some others.
I was excited to see her again but I did not by any means buy a ticket to part 2 because of her. If you see part 1 and don't want to see part 2 unless there's a new star added to draw you in, you probably weren't going to see it anyway. Frankly I'm surprised anyone would want to see this and not plan to see both parts... why see half the story?