Well from what I have seen on the reviews of the 290 series, the 290 is about the same performance of the GTX 780. I'm sorry but I wouldn't count the anandtech "review" because it is not a real test, there's no information about the system, the drivers, there's nothing that prove it was done in equal conditions. Also I'm sorry but the tweaktown isn't what you asked for. You asked for a comparison with a GTX 780 and a GTX 770 which implies reference card and the GTX 780 from tweaktown is surely not the reference, it's a ROG card, the best from Asus.
go on google and see for yourself. Write "Sapphire R9 290 tri-x review" and look for reviews.
I found one that includes the R9 290 tri-x and reference GTX 770, GTX 780 and more. Sadly, only 4 games were tested but it was under the same conditions but it comes from tomshardware and I never found them to be biased after all theses years
http://www.tomshardware.com/reviews/radeon-r9-290-and-290x,3728-5.html
So usually the R9 290 is between the GTX 770 and the GTX 780 but the tri-x cooler (just like any aftermarket cooler) gives a pretty big boost but not because the card is overclocked but because it is not throttled down like the reference so it even beats the GTX titan (regular, not black) with this cooler. I personally own 2 R9 290 tri-x OC and they run silent just like my noctua nh-d14 and they are pretty cold for a r9 290. It's a good card but it's really huge.
But if you are hesitating between a R9 290 tri-x and a gtx card, you should compare with a gtx 780 with aftermarket cooler like the gigabyte windforce which make the gtx 780 about the same as the r9 290 tri-x.
So to answer your question, the r9 290 tri-x is better than reference gtx 770, gtx 780 and a little bit better than gtx titan but with aftermarket cooler, the gtx 780 is about the same as r9 290.
Facebook
Twitter
Instagram