What to wear....

I have a dilemma....I have two weddings in one day! I need a dress that I can wear to both so I don't have to change in between.(I doubt that I could pull a Katherine Heigl in 27 dresses) One of the weddings is black tie and the other is more casual ....what should I wear?

One choice that I was thinking about is the Susana Monaco "China" Dress. It's very beautiful, but 100% cotton which gives it a more casual look.

Any ideas or suggestions?

Jessica