Direct question for Logan/teksyndicate team

Hey Logan, Pistol, Qain, Wendell, I have a question regarding SLI and overclocking a cpu. I have been thinking of putting in a second evga gtx 780 sc in my build but I have been told I need to overclock my i5 4670k in order to get the full power (or at least most of it) out of a SLI setup without bottlenecking. Is this true and if so what would be the optimal overclock for such a setup? My pc specs as of right now are as follows, i5 4670k, gigabyte z87-d3hp mobo (that mobo doesn't support SLI so I got a new asrock z87 extreme4 mobo which has not been installed yet), two 4gb sticks of kingston hyperx 1600mhz RAM, samsung 840 pro 128gb ssd (boot drive for windows 7 64bit), 1tb western digital black, lg dvd drive, 6 case fans and 3 cpu fans on the noctua nh-d14, evga gtx 780 sc with the acx coolers and lastly a corsair rm850w psu that will be replacing my corsair cx750m psu. I know you guys have access to a lot of hardware, so hopefully you have tried a setup like this or at least can give me a informed answer. Thanks in advance for the help. P.S. I'll most likely overclock either way but I don't want to rely on a overclock in order to buy a second card.