Why are you editing this to 960×540, is my question.
Keep it 960×720. DVcPro HD works in anamorphic HD format. It is scaled to 1280×720 upon output to an HD monitor to honor the 16:9 aspect ratio of HD. FCP will try and render a movie that you have set to 960×540. If you keep it 960×720, FCP will not need to render it and will play it in real time. You can create your graphics at 1280×720 and upon rendering them out, they will get scaled “anamorphically” down to 960×720 in the DVCPro HD codec.
You should try that format if you plan on using FCP without a render after rendering from Motion.
Make sense yet?