Some of the HP losses quoted with a mechanical fan are way on the high side (IMO) and usually don't take in to consideration the HP loss caused by the additional 25-30 amp draw that the alternator has to supply. Due to clearance issues with my street rod, I have to run a 16" electrical fan. Draws 24 amps and I can actually watch the rpm drop when it kicks on
30 amps at 14 volts is 420 watts. 1 hp = 746 watts. Allowing for alternator efficiency, belt frictional losses, etc. that's less than 1 hp to drive the electric fan. Even if that 45 hp from the magazine article is double what your experience is, I'll take 1 hp over 20 hp loss any day.
The reason the RPM drops when that little load kicks on is that your idling engine is only making a couple of hp just to turn itself over, so the alternator load is a significant change... same thing happens on a non-computer-controlled car when the A/C compressor kicks in.
