Having two cameras in the scene, one with 'Depthonly' and a lower depth value, there is a severe drop in framerate.

Repro steps:
1. Load attatched project
2. Make sure you are in Metal editor
3. Run the Test scene
4. Press space bar to switch camera depth, notice framerate

Expected results:Framerate should be consistent.
Actual results:Severe drop in framerate, in my tests going from ~90fps to ~10fps

Note:this does not happen in either GLcore or DirectX APIs

Repros in Unity 2017.1.0b4

Retros in 5.6.0ps but is not as bad