Here's the thing I don't like about the implication that it is the fan clutch:

When I pull over while the car is running hot, the lower radiator hose is "cool" to the touch (c.f. the upper radiator hose). I don't have a hard number, but I would estimate that the hose is less than 55 C based on feel. This is the temp at which I pour bottles of molten agarose in the lab on a daily basis, I do know the difference between 55 and 75 C by touch.

If the fan clutch were faulty, then the radiator would not return "cold" coolant. Right? In addition, I would think that the car would run hotter at idle, when the fan is needed most.

A poor circulation issue on the other hand, would produce hotter coolant within the engine and colder coolant returning from the radiator, because the coolant spends more time in each respective part of the system.

As to the source of poor circulation... it could be any number of things: clogged radiator, thermostat not opening fully, weak water pump or clogged engine passages. The first two I think are OK, the last two... I don't know.