FX8320 @ $149,99
Turn OFF Turbo, OC to 4.2GHz and you have the best CPU for BF4 for the price.
it's great value but, the i5 2300 can be used 100% fine with the cheapest MB you can find, and the crappiest cooler, you can use sub $50 MBs just fine with it!
if you are trying to save as much as possible, it's always something to consider, 8 core FX requires a decent MB.
Lowly 4T 750K @ 4.3Ghz is working at ~80-90% util. in BF4 in my case(32-64 slots, doesn't mater). Radeon 6870 (OCed to 940Mhz core) is constantly pegged at 100% util. with pretty high heat output. I wonder how high on GPU I can go before my 750K becomes a bottleneck in BF4 MP? Maybe Radeon 270X?
it's really up to the settings you use, if you decide to play at 1440p with 200% scaling and MSAA... well, you can go really far... but with lower settins it's easy to bottleneck, just luck at the 4300 on that graph, it's a good level I think, but half of what some CPUs can achieve.