Question/request about mineral saturation

Does anyone know at what point it becomes useless to add probes/drones to mineral? Another way to put this, when is the mineral mining saturated? Is there a limit?

for example, gas is saturated (running at full capacity) with 3 probes (correct?)

Also, I think it would be interesting to plot a graph of #probes mining a patch of mineral to mineral mined per second(or minute)