The list of applications that support DirectX 12 or Vulkan isn't very long, and the list of applications that support both APIs is, as far as we can tell, empty. At least, it was until this morning. Futuremark has just announced that its API Overhead feature test, a part of 3DMark, now supports Vulkan in addition to DirectX 12 and DirectX 11.
The API Overhead test runs through a visually-simple scene with an absolutely nonsensical number of polygons. The test keeps increasing in complexity until performance drops below 30 frames per second, piling on up to hundreds of thousands of draw calls. Once that's done, 3DMark records the performance level and moves on to the next API. Futuremark's test has both single-threaded and multi-threaded modes for DirectX 11, while the DirectX 12 and Vulkan tests are always multi-threaded.
We don't make much use of 3DMark around these parts, but having a single application that can run on all three APIs could be useful for troubleshooting, if nothing else. Testing on my own personal machine—equipped with a Core i7-4790K and Radeon R9 290X—I found that the test eked out slightly more draw calls per second in DirectX 12 mode (19 million) than in Vulkan mode (18.2 million). Of course, both were far ahead of the DirectX 11 results at 2.2 million draw calls per second.
Current owners of 3DMark should already have an update pending or downloaded. Those with an interest in getting some numbers from their system can pick up 3DMark at Steam for $30.