Getting high FPS on Flash/AIR games for mobile?

I'm working on a game aimed to be deployed on mobiles as "native" apps, and desktop web browsers.

Since working on several platforms, Flash and its embedded AIR seemed to be a pretty good solution. But uh-oh.

Working only for now with 4-keyframed movieclips (Adding them to stage, updating their position on every frame, and eventually removing them) makes the game to slow down when about 30 are displayed on desktop screen, about 20 when displayed on my Android (Samsung i9000 - 2.3.3). And I may need more.

So I tried blittering, by redrawing regions of my bitmap, and converting my MovieClips to bitmapDatas spritesheets, stored in my Flash library. Results on desktop are great, with perfect, smooth animations, even with hundreds of objects. But the result on mobile is terrible, FPS drops down to 15 even when only one object is displayed on screen, CPU or GPU rendered.

Because it would obviously be nice that my game works on 'old' devices, is working with Flash and AIR a bad idea at this time if I want to reach a framerate close to or above 50 ?

Is there any tips, or indispensable practices that needs to be used when developping a mobile game with flash ? Is there any common mistakes we have to avoid in these kinds of case ?