Performance of Adobe Flex vs Unity for UI

Hey everyone! I recently got a contract for a business app that has a huge requirement for battery life. The app will be running 24 hours a day on a Nexus 7 tablet that will be cradled and swapped with a second tablet only when the battery drains, and I need to decide which platform to write the app in. I want to create it in either Unity or Flex. Having done all of my other apps/games in Unity and Shiva, I would save some time just going with Unity, but in the interest of performance and pre-built UI components, I thought I would look into Flex. I want to use a cross-platform tool in case I decide to port it to iOS.

Does anyone have any current data on performance of Flex vs Unity? Basically everything I read says it has huge overhead, and various tests have shown Unity to run faster than ActionScript, but these are all old posts. I believe Adobe stated that the latest version of Flex was updated to improve performance, so wondering if anyone has experience with that and how it compares to Unity, recently.

The app will basically just sit there most of the time, and I could even disable rendering until the user touches the screen or interacts with it. It will simply be a data entry and data display app, no fancy 3D stuff. But I love NGUI, EZ GUI, and 2D Toolkit, and I'm looking into e-Driven, so I'm comfortable using Unity. I just mainly want to get the best battery life at this point. Any help is appreciated.