I don't usually necro, but seeing as this came up on google, I'd just like to point out that above poster is spouting from his backside: GTX980 is not overkill at 4k, nothing is. The GTX 970 is slightly slower than the 780ti but so much more technically advanced due to newer tech. Upon OCing the 780ti and the 970 you will find the 970 comes out faster in every case.
GTX980 currently doesn't have any AMD rival so Nvidia are overpricing it, so if you really want it you will have to wait from AMD to bring out a competitor. That's when the price will drop.