At 1440p, the R9 290 easily wipes the floor: http://www.anandtech.com/bench/product/1036?vs=1068
Although a minute amount of games (only Bioshock Infinite and Crysis 3) seem to favour the GTX 780, slightly. I would still recommend the R9 290 because 780 only seems to be pulling 1 or 2 frames ahead and the R9 290 proved better (by a wide margin) in the majority of the games.
As someone previously stated, the wider bus memory and the higher frame-buffer really helps it at higher resolutions against the 780.