The difference is precisely jack and shit... Jack, meet shit... Shit, meet Jack. Any questions?
You're right, the higher the electrical demands on a generator the higher its resistance to motion.... the stock fan too places a mechanical restraint on the engine. Any difference is negligible. Both require little to no power at cruising speeds where enough air is moving through the radiator to not only keep temps cool on it's own but to also move the fan.
If you're concerned about reducing losses a flex fan and appropriate clutch are probably the best bet as they're lighter, easier to spin, the blades flatten out at higher speeds to reduce resistance AND they're reliable. Do NOT try to use an aftermarket flex fan with a stock clutch... they spin too fast and the blades may come apart or move forward.
But at the end of the day, MJG's got it, there's nothing to be gained that's worth the effort or expense... unless you're driving a N/A... then you're definitely going to need that whopping 2HP difference.
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.
If you're so inclined I'm always more than happy to accept tips via PayPal. 
Tip Jar ---> 
|