The GTX 960:
I have this one in my other PC.
http://www.evga.com/Products/Product.aspx?pn=02G-P4-2968-KR
I believe it now comes in a 4GB version as well. The card is powerful and runs ice cold. I got lucky, my card runs at 1480 MHz out-of-the-box! Out performs my R9-280 by a good bit from my limited benchmarking I was able to do. And Evga has one of, it not the best, warranty in the business.
The R9-280X:
I have had no experience with an R9 280X. But from the number of posts here about the Toxic, I would say that is the one to get (if your case fits the long card). It seems to be the fastest clocked of the 280x out-of-the-box. As far as any issues with flicker/artifacting, etc... all I know is what I read like you.[/quotemsg
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very hard to choose, what card to get..