atomicWAR :
Shektron :
For playing at 4K you can't go below a GTX 1080 Ti, it's the only card that can do it properly atm.
Not true but more ideal. GTX 1080 can do it with some compromises. Personally I have 2 doing it in SLI so depending on SLI support in game I see both sides of this equation. Generally speaking though a GTX 1080 is the least you want for 60hz/fps with some compromises (game depending some you can max out)...GTX 1080 Ti for max game settings at 60hz/fps (most games but still a few it is not enough)...an argument can be made for a gtx 1070 at 30hz/fps with compromises as well. Then you have to go SLI for things like 4K 60hz max settings in most games, GTX 1080. 4K max setting near all games at 60hz, GTX 1080 Ti SLI. 4K max some games compromises on many others at 60 hz sli GTX 1070.
Well of course, that way a GTX 1050 is also a good enough 1080p card, but I get your point. But someone who wants 4K should generally go for 1080 Ti because that's the only card that is powerful enough to provide 60 FPS in a majority of games. But if you're willing to play at lower details, then obviously you can get away with a 1080, though I seriously doubt 1070 managing 4K in AAA games. SLI is something you should always avoid, unless even the top-end hardware isn't giving you enough performance. Always better to go for a single powerful card, and SLI only if the most powerful card still isn't powerful enough for you. When a 1080 Ti is available, 1070 or even 1080 SLI isn't very sensible.