I have to say, I was really impressed with both Cynthia Ervio and Ariana Grande

They were wonderful in both their acting and singing (expected of course). The thing that really impressed me though was this. I read on IMDB that Cynthia Ervio sang Defying Gravity live while filming that scene, instead of using pre-recorded vocals. I hope we see more of her in the future (for the US that is, I know she's big in the UK.)