Hi Jason,
viz.CULL_FACE doesn't prevent hidden surfaces from being drawn. What it does is prevent both sides of a polygon from being drawn. For example, if you are drawing a box and you don't care about seeing the inside of the box, then you can turn on cull face. This usually doesn't give you a significant increase in performance though.
Usually the bottlenecks involve high resolution textures or high polygon models. When your script is running try checking the stats by clicking on the stats button in the GUI (It's the button that says "123"). It will print out how many triangles there are and how much texture memory is being used in the output window.
If the amount of textures being used is close to the amount of texture memory your graphics card can handle then that might be the problem. Also, make sure the width and height of your textures are a power of 2 (2,4,8,16,32,64,....). You can easily see if any of your textures are not powers of 2 by checking the output window. It will display a message like this
"Scaling image '<filename>' from (<width>,<height>) to (<powerof2width>,<powerof2height>)"
The viz.framerate() command doesn't return anything. It just tells vizard to display the framerate.
Let me know if you need any more help.