I don't have the specific numbers you are looking for. I don't currently have a Rand head. You can test for yourself. When you start the machine, both hoses will start getting warm. You will feel the heat rise up both hoses very slowly. The rear hose will rise slightly faster. Once the heat reaches the radiator's top tank, you will be able to feel the lower hose go cold and the radiator will get warm. This is when the cold water in the radiator dumps into the head. The water will start flowing faster from that point. If you have a water temp gauge in the head, it will read different temps when the water starts flowing depending on how the engine is heated up. If you start the engine then flog it, since the water if not flowing, it may hit a higher temp than if you let it warm up. I don't run a fan at all. If your setup requires a fan, then if the water is flowing at all, the fan is reducing the water temp in the radiator. The engine produces a fixed amount of heat energy. Slower flowing water will result in a larger heat difference between the inlet and outlet of the radiator. So if the water going into the radiator is hotter, the fan will drop it more.
Cylinder head temperature is the important number. That is the end all number. Water temp, flow rate, efficiency of the head to transfer heat to the water are all just factors in how well the entire system maintains the temp of the head. A bone stock air cooled machine can hit 450 degrees cylinder head temp and will experience a power loss. My own machine hit 325 while full throttle doing donuts in heavy mud. Within seconds of the throttle being let off, it dropped to 250. Stopping, getting out and idling, it drops to 200. This was done with straight water that did not boil. If you want to know how well your cooling system works, install a CHT.
Colder head temp is not better. People who have installed an electric water pump with an Aftershock head have found that the engine will foul spark plugs.
