Thanks Andreas. What a privilege to get a reply from one of the top men!
I was hoping to update the first post with details, in a tabular format for easy comparison but it appears this board neither accepts standard HTML table tags or any BBCode version. Perhaps a Wiki would be a better place. Does Adapteva have a wiki? If no, perhaps might be a good spot. It already has and others.
Regarding a GPU, if the Parallella doesn't have one, how does it output video to the HDMI port? Does the ARM chip do that job? I had a look at and I can see references to "NEON / FPU Engine". The references plenty of multimedia capabilities. Are these instructions what allow the ARM chip to output video to the HDMI port?
Alternatively, are the Parallella boards only really meant to be used in a headless style, with the HDMI port merely there for diagnostics? Speaking of which, is the missing a reference to the HDMI port, or am I missing it?