There are no plans at this time to release RenderPro for CX 6 or 7. There has been less and less demand for RenderPro as Design 3D's rendering speed has increased, and computers have gotten more powerful.
You may be interested in checking out the benchmarks page on the StrataCafe: http://www.stratacafe.com/benchmarks.asp This page allows users to post their rendering speeds on different machines, with different versions of Design 3D; all with the same model and render settings.
Remember, you can render in the background, and use the Rendering Queue for multiple renders. For more information see the User Guide, which is located in the Help menu.