UI Overdraw Test Opaque vs. Transparent

I've been working on optimizing UI recently and today I did a test to see if using opaque shaders would make any difference. I made a scene with sets of 20 nearly full screen images overlapping one another rendered with a varying degree of shaders. I modified the normal Image shader as well as the "fast" shader found here https://unity3d.com/learn/tutorials...s/fill-rate-canvases-and-input?playlist=30089.

Surprisingly in both the fast and default UI shaders I...

UI Overdraw Test Opaque vs. Transparent