will amd 7990 be enough for 4k resolution ?



Many of the aftermarket 780 ti's perform much higher than the stock 780 ti's. While they probably won't beat a 7990 on average, they are close, and don't have the draw backs that come with crossfire. They are also much quieter and have a good amount of OC headroom. When compared with an OC, the 780ti improves much more than the 7990 (the 7990 doesn't OC well, and thermal throttling pretty much kills it).