I would say your good, if you wanna save money, get 3 290x's. What i will say is make sure you turn down or turn off AA. At 4k those kinds of corrections are far less important, but they also are the hardest part of runing 4k. Running AA on 4k basically samples 4x the number of pixels each time. so i would use minimal or no AA. that will get you better numbers than the benchmarks.
Also, if i may ask, which TV are you getting. And what games will you be playing? (I not only build PC's but I'm the salesman that trains the other salesman for my local Magnolia AV).
The thing is, if you buy a Sony 4k (like the 810c or the 850c) u can use the upscsaling algorithms to do AA for you. basically, you turn on your upscalers (not all the way) and then render at like 1440p (or any 16:9 aspect ratio) thats higher than 1080p but not yet 4k and let the upscaler do the last step of the process. It'll give an AA effect and give you computer a break from the processing.