Ironically, given the context of this discussion, those people whose bodies maintain a higher differential (what you called poor circulation) are more efficient

Ironically, given the context of this discussion, those people whose bodies maintain a higher differential (what you called poor circulation) are more efficient at maintaining their core temperature in other circumstances. For example, you are out walking on cold ground. Your feet get cold while your core stays warm. This is ideal for keeping heat in your core. You may survive where those with "good" circulation would lose heat too fast. Although this may be due to lower rate of blood circulation, there is another effect independent of circulation rate. Heat-exchanger effects along limbs depending on the layout of your veins and arteries, which varies among people. The extreme example is penguins, whose feet are on ice yet their bodies retain heat because of heat exchange as blood circulates in their legs. It maintains a temperature differential along the legs. I'm not suggesting people have specific anatomical structure like penguins, rather I'm saying the natural variation in the placement of veins and arteries in human limbs will result in a range of heat-exchange factors among different people, which is a separate factor from circulation rate, and may indicates a thermally efficient body for some situations.