Until there is a DX12 API, having a DX12 capable GPU isn't going to give you any gains you can use that couldn't already be had from DX11 equipment. Also, unless DX12 comes with new features, DX12 hardware still may not benefit much as my understanding is that DX12 is more about reducing the API's overhead than a new feature set. I fully expect gains from a release of DX12 to be beneficial to older, non DX12 equipment, but time will tell.