I suppose it also matters how much light you have in a scene. If there's enough that the scene doesn't need too much light bouncing around (for example in your test 1 and test 2 in your first post) you can probably get away with fewer bounces. The images I posted show that increased diffuse bounces may be more preferable if there is only a single light that doesn't give a direct light to the scene.

I also just noticed that there is almost no reflection of the cup in the shed window with no diffuse bounces, yet there it is with 10. That may be another thing to factor into your bounces number.