I am honestly pretty much clueless on these type of lighting things, so Idk if my response is even worth giving.  But  I'll try anyway.

Could you do two different renders of the exact same scene - change nothing but the raytrace bounces and then open those images up in photoshop.

If you go to adjustments - curves, a graph is shown that I assume represents the levels of light in the image.  SS your graph for each and then lay the SS over each other.  If there is a difference in the graph, maybe that is the proof of difference.

Now mind you I could be WAY off the mark on this.  Hopefully BB sees your thread.

I am:  aka Velocity3d