Also on My RIG Mantle is Great:
I'm Playing with API Mantle in BF4, Thief, DA:I (but reversed to DX11.1 cuz i need SweetFX :D ) CIV BE -> every Game runs smooth.
Also in BF4 Multi when Levelation occurs in DX11.1 drops from >75FPS to 38FPS but in Mantle is stable >60FPS
And YES DX12 and Vulcan...