I am no professional in this area, although I have read about a similar subject to this. Running GTX 780's in 2-way sli, should be ran with atleast a 850 watt psu, and an FX-6300 is probably going to bottleneck the GPU's. I don't know what CPU you'd rather get, but you should definitely look into getting a better CPU. My guess is somewhere around an FX-8350.
Disclaimer: I am no professional as previously stated, this is all based on what I have read from other professionals, I am just forwarding tips and knowledge.