Tested AMD's new Mantle thingy in Battlefield 4 just now, and as you can read in this reddit thread here, the results are mixed. For me myself, I am using an Intel 4770K + Sapphire Radeon 280X, and there were minimal to no FPS/Performance increase at all. I even ended up having multiple stutters and frame drops along the way, something everyone also noticed. In fact, in some cases it's better to use DX11, especially in maps where debris and smoke is apparent

Might need a few more driver updates before mantle becomes mature IMO.