Sorry, saturation is not the right word to describe it. I was thinking of the ice/water analogy and I mistakenly applied it to my heatsink analogy.

The correct limit to the heatsink analogy would a function of the thermal dissipation of the heatsink (material, surface area, thermal resistance) and the qualities of the surrounding fluid (ambient temp, flow, etc). Honestly, my comparison between the ice/water example and heatsinks is not good. It is only appropriate in reference to the “molecular collisions” concept I mentioned before.