On the "good news" front the nMP will finally get those long, long predicted GPU upgrades.
By the miracle of "badge engineering", AMD doesn't have much in the way of new stuff, so they'll promote some of their old chips up the line. I already saw that Pitcairn (D300) is getting a shiny coat of oaint and a new name from new series.
Perhaps D450XXZ ? Does that sound fast enough or does it need another "Z"? Or maybe an "S"?
The 5K iMacs have a real "scorcher" in the form of a GPU that sits at 105C if doing anything that requires 3D or video playback. Apple hasn't learned that having one chip on a board running 30-40C hotter then all the rest leads to trouble.
Even with a furnace fan blasting heat out of the case, the radiated heat keeps radiating. Those lovely 5K displays will eventually have brown spot or delamination of LCD layers.
Using AMD chips makes great sense when in the boardroom looking at profit statements. Better hope those 5K folks don't bother with AppleCare.
Been able to use an R9 290X for awhile. There are kexts for many AMD cards, if and when AMD releases something other than leaked hype we'll find out if worth thinking about.