I don't think its as far off as these guys make it seem.
I mean dual GTX 670s and 7950s run games just fine at 5970x1080 (bezel adjusted multi monitor res). You may have to use FXAA and lower some of the filters but 40-60 fps isn't an issue for most games.
4K is about 20% more so dual GTX 780s would be plenty.
Benchmarks like this that "max" out games for the sake of maxing out are cool...but not an accurate representation of PC gaming. Unless you like to waste power, generate heat and have lower frame rates with little to no benefit...its recommended you adjust the game's visuals.
Also, a lot of those cards are taking because of VRAM. At 4K you need more than 2GB for sure.







