5K iMac - bad GPUs?

That's the logical thing isn't it. I've got until the 9th January to request a return (Christmas purchasing thing) but doubt I'll get a Genius appointment before then. I might just send it back and ask for a full refund in that case. The problem seems oddly widespread, which is definitely putting me off buying another one.

No appointments near me before my 14 day return window, unfortunately.

It does seem to be "relatively" widespread. I've now had users with the rMBP 650m complaining of the same issue - only since Yosemite.

I'll continue looking around and trying various things. Ultimately, I'll have to decide whether or not to send this thing back.

I chose to return my iMac after being recommended by AppleCare to return it or take it to a store - twice.

Besides a number of graphical glitches, I experienced the more common GPU heat problems...I don't know if the two are connected as I didn't have time to test. I was told, however, that many of the graphics glitches (those you are experiencing) are fixed in 10.10.2 by a couple of beta users.

My primary problem was; The M295X GPU is running hot doing any kind of mid-heavy tasks and in a number of cases is actually throttling itself because the iMac cannot dissipate the heat fast enough. More info here. This could be a driver issue, but it could be a hardware thing. No-one knows.

I asked AppleCare if >100C was safe for the card and was told that temperature is "not safe for anything". That was the tipping point for me. Many users are getting 104-106C on their cards, including me - I actually got it to 108C.

None of the refurb units have contained a M295X, which is also very odd.