How much can you get each of those CPU's for? How much are you willing to spend? Answer those two first and you will be closer to picking between em.
The situation with BF4 is very similar to what we saw with Crysis 3. The game use's two threads to do most of the rendering and spawns additional threads to handle environmental destruction, physics and various battle effects. The more things you have going on the more cores the CPU needs to have, BF4 seems to use about six during heavy battle.
With games like BF3, BF4, Crysis, ect.. you need to completely ignore average FPS and only look at minimum FPS. Average includes staring at walls, the ground or other scenarios that don't have much happening, minimum is what you can expect when stuff's exploding all around you and your fighting back.