You can use these: https://forums.macrumors.com/threads/list-of-mac-metal-games.2045606/
But no game or benchmark currently takes advantage of the Metal 2 features.
Consider also that benchmarking Metal is actually quite difficult since V-Sync is forced and cannot be disabled. Considering that the benefits of Metal can only be seen in CPU-bound situations, the best way to compare performances between APIs/OSes would be to play at low resolution and without AA (which only uses the GPU), use some FPS counter, and superimpose the fps curves.