Brad Wardell, the CEO of Stardock, shared benchmark results of a comparison between DirectX 11 and DirectX 12 on an Intel Core i7 eight-core system with an unreleased AMD GPU in CrossFire configuration, probably the Radeon R9 390X if we'd had to guess. The results are impressive and Wardell says DX12 treating multiple GPUs as a single identity makes a big difference.
Did a test of DirectX 11 vs. DirectX 12 on an unreleased GPU with an 8core CPU. DX11: 13fps, DX12: 120fps. Lighting and lens effects.