All three of those claims are false.
The mechanical fan is clutched so it does not consume much power when free wheeling. The only time its locked is when the engine is above 90*c. The electric fan still loads the engine by loading the alternator when its on.

If you are not overheating then the mechanical fan does not consume significant power, replacing it will not return anything but psychological gains and what minimal amount of fuel it does save will never be enough to cover the cost of the fan conversion. Gaining 1hp is not worth blowing $350!

At highway speeds the fan airflow pales in comparison to the natural airflow through the radiator caused by the vehicle moving, thats why MB limits the fan speed to 3500rpm. Above that RPM you'll be doing in excess of 75mph and the fan could never keep up with natural airflow let alone exceed it.

The only time an electric fan would have an advantage over the mechanical is at slow city or traffic jam speeds. In that case you would still be much better off upgrading the front electric fan and adding a temperature switch to its circuit.

If you want a worthwhile upgrade to the stock 5-blade aluminum fan, swap in the smaller waterpump pulley and 9-blade plastic fan from an 84-85 model. The plastic fan has less mass and moves more air and the smaller pulley (0.9:1 instead of 1.09:1) moves more water, both combined make for much better cooling performance. (Bo NOT use the smaller pulley with the aluminum fan or you could end up with fan failure and blade holes in your hood!)

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