I just got a second AMD 7870 on black friday to add to the one i had. So i now have 2 AMD 7870s in Crossfire. My CPU is the AMD Phenom II X4 955 BE (OC to 3.6, stock 3.2). Mobo is the ASUS M4A79XTD EVO (Crossfire certified). I tried all the different AMD drivers starting from 13.9 to 13.11 betas. In Battlefield 4 both my GPUs only use 30% of usage and my game runs at 30-40fps (graphics rating from low to ultra doesnt change anything). Is this a BF4, AMD Driver, or bottleneck problem? I tested my video cards on other games like Counter Strike: Global Offensive, Natural Selection 2, and League of Legends. I had huge increases of performance on those games and my GPUs were running at 99% usage. So what is going on?
I had a 965 BE and a single 7870. I was getting 40 FPS. Then I upgraded to a FX 8350. I now get 70-80 FPS on Ultra. So yes it's a bottleneck issue. BF4 recommended requirements is an AMD 6-Core CPU.
Best of luck!
If lowering quality doesn't effect FPS it's usually CPU related.
On another note I had the same issue in BF3 with a i5 2500k running at 4.8ghz and 2 6970's, updating my motherboard BIOS fixed it.