Love your question and I must admit, I've never even considered the answer before you posed it.
For me, there is no need to reconcile the two. There is no reason that women cannot possess both qualities in equal measure. If we buy into the stereotypical notion of the Feminist, that was born out of the 60s, as being a tree-hugging, hairy-legged, fiery liberal, I think we are selling women short. Women are complex, magical creatures. They can be equally sensual, sexy, and magnificent in their femininity while simultaneously being committed to equal rights and justice for their gender. They can be equally beautiful and intelligent, they needn't aspire to be merely one or the other.
Femininity and Feminism are two different weapons in a woman's arsenal against a male dominated society. Both may have equal effectiveness but are used in very different ways at different times.
I'm not exactly sure what you mean by femininity as a "performance." I think that women are either feminine or they are not. It's the same with men. Some are vastly more masculine than others, but I do not feel that, for the most part, masculinity is a performance. Sure, there are both men and women that strut their stuff and use their sexuality to their advantage. We do it to attract partners of the opposite sex. We do it to achieve the desired outcomes in business, or to win debates, etc. I'm not sure I'd call that "performance," as much as "manipulation," but maybe that's just semantics.