He Jim, is this a final render or preview? I can handle 8000x8000 as well but only if I render... in the preview window of the scene is nothing to see...the model turn to black as in your render.. If you render bigger image as for example 3000x3000 300 dpi you will see the effect and that what get about to allow the commercial people render super quality commercial renders.. I have always the same problerm If I have to do a cover for custom work with lower versions in this situation 4000x4000 don't help me much and I have to work for hours with postwork..