I have an R9 270X Dual-X OC from Sapphire. In Battlefield 4, I am running multiplayer at High settings at about 40 fps. I am on DX11, should I switch to Mantle? I have seen the 270 run BF4 at ULTRA settings at about 50 fps. I have tried stock clocks, small, medium, and the maximum safe overclocks with the same result! Any help would be much appreciated. Ask for more info!