Regarding that you have completely changed the way it renders all the stuff, we could expect some problems, but anyway, despite of all of that, you did the great job and a lot of people (including me, of course) are very grateful to you for your incredible work. As to performance, I myself had tested my game with the new Starling, and, yes, it works much slower, but I have quickly switched back to Starling 1.8 for now, so it's no problem
I think 2 things that should be changed now are:
1) Remove default pixel snapping. It's a good feature, but in most games it affects the smoothness of animations. That's where we have to compromise between the sharpness of images and smootheness of animation. I, personally, stand for the second.
2) Make some clear way to disable render cache. It makes some animations become jagged, but I couldn't find a way to disable it on my own