Thanks to the new Stage Video feature, Adobe is now claiming that the latest version (10.2 beta) is 10 times more efficient than version 10.1.
The Stage Video feature is an API that delivers high performance video playback across platforms and which can shift most of the work for Flash video to the GPU.
Unfortunately, Stage Video requires Flash developers to update the code in video players so your at the sites mercy as to whether or not you will benefit from the new feature.