The 260X isn't great for BF4, but your system is well balanced. The cpu will handle multiplayer okay, but the 260X will struggle to keep a very smooth fps, even while in medium settings.
It's hard to judge exactly what fps you will get, as every system is different. But I would say about 40-55 on medium in a 64 player server on a large map.
Expect 10-15 fps more in BF3 than in BF4.
This isn't exactly butter smooth, but is playable and I hope you enjoy playing the Battlefield games as they are amazing (despite the netcode problems still)
Hope I helped!