based on this article by werner sharp from the adobe engineering team i tried creating a typed array storing 16bit uint’s in strings (the 16 bit limit coming from utf-16). the getITemAt turned out to be quite a bit slower than i expected and peter then suggested using bytearray to do this as well.
the experiment is posted here, the code is availible via the context menu.

using any tool to monitor your flashlog you will see the results. included you will find some unit test using asunit

the results:

Array test
added 10000 items  1
retrived 10000 items 1
altered 10000 items 0
byte array test
added 10000 items  2
retrived 10000 items 2
altered 10000 items 2
string array test
added 10000 items  8
retrived 10000 items 3
altered 10000 items 4005
wow, arrays in AS3 are just super fast!