Stan, totally on point here, as usual.
A powerful engine(150hp) is going to run lower temps when lightly loaded, as in highway usage, than a stock 60hp mill that has a LOT more throttle(and load) in the same situation.
What heads you use(which casting matters) and complete engine configuration has more to do with head temps than fan speed. What fan housing/pulley ratio/fan/flaps/thermostat/oil cooler are factors as well.