This means the stock r9 290x cards are better than stock gtx 780. Get the r9 290x.
But the 780 has better overclockability. When overclocked it beats even the overclocked r9 290x almost in every game. Example: Crysis 3 on very high- GTX 780(OVERCLOCKED) 44.6 FPS, r9 290x(OVERCLOCKED) 40 FPS.
Don't know about that. Then take the 780 with best cooling solution and overclock it to your wishes..
But of course there is no guarantee you will be able to overclock your GPU up to the values you have seen on the internet, so good luck