If you're using Quicktime mov as a wrapper you can't set your data rate for video, just your overall quality (on a scale from 1-100). You also can't set you audio data rate when using the Quicktime format.
If you want to control your data rate for video/audio, use the h.264 format (instead of Quicktime). That will make it a mp4 wrapper. If you have to have a mov wrapper you may need to look at something like Sorenson Squeeze or Telestream Episode to get what you want.