DICE's recommended hardware list for Battlefield 4 includes quad-core Intel CPUs and hexa-core AMD processors, suggesting optimizations for threading that we typically don't see from games. So, let's see how different CPUs and architectures handle the game:
While we see a clear performance drop from the FX-4170 and Core i3-3220, frame rates remain comfortably above 40 FPS. That's great new, though if you own a GeForce GTX Titan, you probably wouldn't be enthused about that 20 FPS-drop attributable to too-slow of a CPU. This beautifully illustrates the importance of balance in a gaming PC build.
There's a noticeable speed-up going from FX-4170 at 4.2 GHz to the FX-8350 at 4 GHz. Although AMD doesn't fare as well as the Core i5s and i7s, we can at least speculate that Battlefield 4 does get some utility from a six- or eight-core CPU that you don't see from a quad-core chip.
It's also interesting that Sandy Bridge-E delivers the best minimum frame rate, despite a relatively slow operating frequency. That has to be attributable to lots of L3 cache or core count. Why the bunch-up around 74 FPS on average? That's the GeForce GTX Titan bottlenecking performance. We'd need a dual-GPU configuration to push Battlefield 4's frame rate higher.
The lower-end processors certainly encounter spikes in frame time latency. But keep in mind that this is the Ultra preset, and that a less demanding setting would likely help smooth some of those out.