At one time I followed the same logic but that's not how it works. Heat is always transferred the fastest when there is the largest difference in temperature; the hotter the antifreeze in your radiator (OR the colder the air outside), the faster the heat is being absorbed by the air flowing through the fins. So you actually want the coolant flowing faster so that the temp of the water in the rad is always as high as possible; that will reject the most heat. This is also why using a colder thermostat actually puts more load on your cooling system and can make it easier for your engine to overheat. The t-stat opens when the coolant in the block gets up to temp and lets the coolant circulate until the whole system cools down again; that takes longer the lower the temperature the t-stat is rated for.
