I was planning to do some test about it myself. Just so I understand what method you are using, let me see if the basics are correct:

1. Sprite Pooling.
*You have separate sprite object for each arrow.
*Bitmap from memory is loaded into each arrow bitmapdata object.
*Arrows are added to stage using addChild.
*Arrows are moved by updating their x and y properties.
*Scrollrect property is changed for each arrow at every step.

2. Copy Pixels
*1 general arrowsprites bitmapdata object is created.
*You have general object for each arrow (not the sprite object).
*Arrow sprites are not added to stage.
*At the stage is visible just 1 big bitmap object.
*Arrows are moved by updating their x and y variables.
*Main bitmap is cleared at each step.
*CopyPixels is used to copy image from arrowsprites object to main bitmap into position of each arrow.

Is the description correct so far?