Yes, all GPUs since Fermi support DX12. GTX460 and up. Not 100% sure what exact DX12 features they are talking about, but neither Nvidia or AMD have full support for it yet. AMD is significantly ahead on this front with their GCN cards is my understanding.
Real world performance is up to the game developers to implement. It will vary by game, and obviously they aren't going to go back and re-work older titles, so what you have now is what you will get going forward with DX11 and earlier.
Early numbers look quite promising, but effectively you are still limited by the GPU.