Mechanical Fan VS Electric Fan

The fan has resistance that requires energy to move.
When the motor is used the resistance is in the motor causing it to work a hair bit more taking away hp to the wheels.
When an electric fan is used all the resistance is in the electric motor. Not on the motor. It doesn't make more horse power. It frees up the motor to deliver more hp to the wheels
Putting more in the alternator will not cut hp per say. It doesn't tighten up causing your more to work harder. Instead it will overwork the alternator causing it to fail early. So when I run big stereos in my cars I upgrade the battery and once the alternator starts going out I replace it with one that can deliver more amps.
If you can afford it if suggest going electric fan. Less stress on your motor the longer it will last. The hp gain is minimal for differences.
Now one thing think about tho is that for every 11 degrees you lower under you hood you gain 1%more hp