Well I think you mean to reverse the parts in the way you wrote the question. In 3d gaming the CPU would "bottleneck" GTX 970 SLI . The Data is being processed by the CPU then the CPU issues commands to the GPU. But to make a long winded conversation short, no your i7 4790k is fine for any GPU in SLI at this time.
Note: there is exceptions , Frostebite 2.0,3.0 game engine is said to utilize 6 cores.