They are correct about the 980 Ti, and the 970. I have all of them, and still see games crashing in 4k. They are correct in that article at PCGamer that you can do 4k, but there are still issues. Number one is that most titles were created with options that are still not possible at 4k (the Supersampling option for one). You can use SS, but if you mix it with other options like AA, or 4K textures you could easily fill even 6Gigs of memory. SS usually comes with options to render at SS 2.25, or 4.0, which is 1.5 times higher resolution, or double resolution. If you mix 4k textures, 4k shadows, AA at x8, and SS at 4.0 you are going to crash your game. The whole point is to determine the limits and once you find those limits leave the options alone. You do not need 4k textures at 4k resolution, or AA either, so you can save yourself a lot of room in memory by just turning those off.
Since you are planning on sticking to HD resolutions the 970 is perfect for you. The commenters in the PC Gamer 4k topic failed to see the one advantage in 4k gaming that is important to someone in my age category. Screen size makes it easier to aim.