To reproduce:
1. Open attached project;
2. Turn off "Use Defaults" in Graphics Settings Tiers (Edit > Project Settings > Graphics > Tier Settings);
3. Build project on both 5.6.0p3 and 5.6.0p4 versions of Unity;
4. In SteamVR, open Settings;
Note: Make sure SteamVR Home Beta is disabled (General > SteamVR Home Beta) for better testing;
5. Go to Performance > Display Frame Timing;
6. In the Frame Timing window, check Details and Total GPU;
7. Open build of Unity 5.6.0p3, look at the Frame Timing Window;
8. Close the build;
9. Repeat steps 7 and 8 with the build of Unity version 5.6.0p4.

Result: GPU time is higher in version 5.6.0p4.

Note: seems to reproduce only on Nvidia GPU, doesn't reproduce on AMD.

Tested and reproduced on Oculus DK2.

Reproduced on versions: 5.6.0p4, 5.6.2p1, 2017.1.0f2, 2017.2.0b1.
Not reproduced on version: 5.6.0p3.
Regression introduced on version: 5.6.0p4.