Id say it aint worth it, unless you switch to x99 build 5820k.
fx 8320 oc still very capable of maxing most every game out there 60+ Frames
and the oc, you should be able to get a lot more out of that cpu.
Also NOTE that dx12 will probally further the life of your cpu, as newer games using this api should be less dependent on cpu. And it should also make it easier for developers to take advantage of 8threads, though that doesnt guarntee it will happen any time soon.
If you absolutley want to make the switch right now, id say just go for the 4790k + decent z97, or Xeon 1231 and pro4 h97 for much cheaper, yet very similar performance.
Depending on the gpu you have now, you would probally see a better increase in performance upgrading that, however just around the corner is amd's 300 series (not their rebrands on oems)