Depends, what are you using it for?
Battlefield 4 uses more than 4 cores, so the more the merrier.
Rendering and multitasking can chew up your CPU cores, so using Adobe After Effects and PhotoShop would be easier with 8 cores.
Running VMs would be smoother with 8 cores. But I would suggest an 8350 if you are going to upgrade.
All the best,
Im using it for gaming, from old to new games, like BF4, or Skyrim with mods and Minecraft with Shaders, and using Adobe after effects, and NUKE, not at the same time, but if i choose the FX-8320, do i need a more powerfull motherboard than the ASUS M5A97 R2.0??