Same exact system, same architecture, and graphic driver, do you see the discrepancy in performance, the spread is close to 15%, that definitely does not fit under normal manufacturing irregularities in my book.
Look, I talk from personal experience, check the unigine thread in our very own forums, I tried to max out my card, and my system was beat by Ivy Bridge and Sandy Bridge systems with even less OC than my Haswell CPU, the difference was so big I just quit trying to get more performance from this card.
It's so bad that my original intention was to put this card under water, but why invest all that money for a lemon? I finally just decided to get an Arctic Hybrid for it and call it a day.
This is me, a 290X owner speaking from personal experience, there are way too high discrepancies between 290X cards in the wild, and this article opened my eyes to the issue, the solution, like many others said before is to either get a third party cooler or don't get a reference card at all, sad but true, I learned my lesson the hard way unfortunately.