As far as I know N900 does not have proper vsync support so there is nothing we can do for the tearing. On many occations it runs around 50 fps but because there is no vsync and the display refresh rate is only 30 fps it's impossible to make the game as smooth as on devices with 60 fps screen and vsync.

In general I still think N900 is one of the best versions of Angry Birds performance wise. I have N900 as my personal device and I've had zero issues with performance, at least when it's the only application running. If you keep dozens of applications running on background it will of course have ill effect on the performance.

Hopefully one day all devices have tearing free 60 fps displays and enough CPU and GPU power to feed it, but until then we just have to play with the hand we've dealt.