I don't know if this is just a PC thing or not, PJF. My test with the demo had many of my B4 files taking more than twice as long to render with no visible improvement in the image (although I did notice other minor differnces in some of the image renderings). Interstingly, the image that rendered much faster in B5 contained an awful lot of transparency and reflection. Yet the speed improvement in B5 versus B4 was better than the improvement people have reported for their Mac versions. I really have not done enough comparisons to offer opinion yet. But it is possible that the speed differences may be due more to the type of scene being rendered than to hardware platform differences.