Some image-performance questions (jpg vs png, smoothing, image size, etc)

I've done quite a bit of digging but it's surprisingly difficult to find informed answers to these questions.

I'm making a Flash game with a friend; as far as we can tell, the code is fine, but there are some serious framerate problems that seem entirely related to the graphics.

• Is there a performance difference between Movieclips as JPGs and PNGs? Most of our graphics are imported as PNGs because they have transparent sections, but I don't know whether there is a performance difference between setting image compression to JPG or PNG within Flash itself
• Does turning on "Smoothing" for an image affect performance?
• Obviously larger graphics have more of a performance hit, but is there any benefit to splitting a large image into pieces? Example, changing a 2000*1000 background into two 1000*1000 pieces?

One thing is most of our graphics are as much as twice the size in the library as they are displayed onscreen, then scaled in the code. We had wanted to make the game still look good when zoomed in/fullscreened but that doesn't seem practical so I'm planning on resizing all of the image files to their final size in the game and removing the scaling code. Hopefully that's the major part of the problem.