This Unreal Engine 4 demo shows the engine's capabilities using DirectX 11 with demanding particle effects. Before running the demo you might have to install the (included) Microsoft Visual C++ Redist Runtimes. Settings can be edited using the included batch file (e.g. ResolutionSizeX=1920; ResolutionSizeY=1080).
The newest UE4 version supports DirectX12, keep in mind that the dx12 is still in development. Video after the break.