Is a btn symbol more memory efficient than mc symbol?

Hi,

I have about 20 thumbnails images, with a roll-over effect on them, that automatically scroll across the screen. Each one when clicked brings up a pic of a portfolio piece. I have made them as MCs. But they judder from time to time in their movement.

My guess is that it might be a bit too memory intensive for Flash player to move all these thumbnails at once. Would making the buttons into btn symbols improve the movement? Or is it be due to something else?

Generally, I am surprised that it is not a smooth ‘scroll’ as I don’t think the project is that complicated. The project is at 30fps. I have tried it at 20fps but looks the same.

The project is at http://www.frostell.com/

Thanks for any help.