Lemme see if I remember . . . that's the low-end hex-core Ivy Bridge K processor? And you want to use it for a server on your LAN, is that right?
Test the power supply, or -- if it were me and I were using used parts to build a "new system" -- replace it with one of lower wattage spec -- maybe 650W or 750W. Or simply use a PSU calculator based on the number of devices, processor, overclock, RAM etc. and get the improbable "all-devices-at-once" minimum. You might only need a 550W.
Then, pull the GTX 780 Ti and either redeploy it, sell it, mothball it. If you need a graphics card at all for something that can actually run "headless" once configured, and since the X79 mobo doesn't have a graphics function because the CPU lacks an iGPU, find a low-end $50 PCI-E graphics card which also uses less power. It just seems that the 780 Ti would be wasted on a server-as-NAS. I think I'd actually spend the money on a low-end gfx card, sell or redeploy the 780 Ti, set up the system initially with the low-end card and then remove it if I can run the server headless.
I'm guessing -- with no personal experience -- that FreeNAS can be accessed headlessly from a workstation. For myself, I'm slowly replacing a WHS-2011 server on a 680i mobo and Q6600 processor. I chose to buy a license for MS Windows Server 2012 R2 Essentials. I will feel more than overpowered for just using an i5-3470 and 16GB of Corsair XMS. Since it has built-in graphics, I can turn off the motherboard SATA controller, and add an 8-port Super-Micro SATA-III controller with basic RAID options to use in AHCI mode with pooling. I could add a second 4-port or 8-port card on the Z68/Gen3 motherboard, and still use the third PCI-E slot for an x4 device or controller. And of course I could use the onboard Intel controller and any combination of the storage controllers I only mentioned by example.
It depends on your business and activities. That's really a high-power configuration for building a server out of "old" parts.
It must've been short of 3 years ago when I was planning and doing the initial parts-option spreadsheet for an X79 system with that very motherboard. It just didn't seem as cost-effective as the Skylake I just built, and I chose to wait through Haswell and its E model. There were some two more plans before I settled on this.
The tempting thing for me about a 7700K is the overclockability factor. I think some of those in the upper silicon lottery will run at 5Ghz on good air cooling. Otherwise, the consistent performance improvement in every area except for power consumption over the 6700K doesn't seem worth the outlay for a Kaby Lake.
But for you? Absolutely.