Actionscript 3 :: Create A Fast Endless Scrolling Background

I'm trying to create a endlessly scrolling bitmap background. I want to make it as efficient as possible as there is plenty of other game logic going on too. The idea is to have a repeatable bitmap scroll horizontally on an endless loop, which can obviously be achieved by placing two sprites of the same bitmap next to each other and offsetting one when it reaches the far left boundary. I was wondering if there is perhaps a faster more efficient way to do this, perhaps using scrollRect or copyPixels? If anyone has any idea which method would be fastest,