NVIDIA has made quite the strange move overnight, where the company has enabled DX12 support for their older Fermi GPU architecture, enabling DX12 for the GeForce GTX 400 and GTX 500 series graphics cards.
If you've got an older GTX 400 or GTX 500 series card, you'll need their latest GeForce 384.76 drivers, which will enable DX12 support. WCCFTech re-benchmarked their older GeForce GTX 580 with DX12 and thrown it into 3DMark and Battlefield 1, but there is a performance drop with DX12 enabled in BF1. WCCFTech's benchmarks show BF1 hitting 43FPS average or so with the High preset @ 1080p, while the GTX 580 with DX12 enabled drops to just 34FPS average.
Still, DX12 enabled on Fermi is an interesting move for NVIDIA... very interesting.