Here are the results from a performance comparison made by NVIDIA on an Intel Core i7 5930K system with 16GB DDR4, the GeForce GTX 1080, Windows 10 64-bit and a 3840 x 2160 pixels resolution.
They compared the performance of the GeForce 368.81 driver with the upcoming GeForce 378.74 DX12 performance driver. Pretty impressive if this is accurate, it significantly improves the Pascal DX12 performance:
Ashes of the Singularity, Crazy Preset: 46.5fps to 50.9fps => +9%
Tom Clancy's The Division 1.6, Max Settings + 1x SMAA Ultra: 31.5fps to 32.7fps => +4%
Hitman, High Settings + High SSAO: 50.6fps to 62.1fps => +23%
Rise of the Tomb Raider, Very High + 2x SSAA: 20.5fps to 27.2fps => +33%
Gears of War 4, Ultra Preset: 41.2fps to 45.2fps => +10%