In order to get it right, normally I have to render a few times and its a bit annoying. Is there any other way to show the entire render frame or could this option be available in future releases?
The render safe frame is a proportion that matches the width and height set for the render output size and not an indication of the actual dimensions. If you float a viewport, by either NewFloatingViewport or by dragging a viewport off towards the command line (after clicking on the viewport name), you can size the floating viewport so that you can see the whole safe frame. This will allow you to see the full rendered area even if the output set is greater than the visible resolution of your monitor.