I was reading the May 2000 'Car Craft' and I came across something very interesting. They did a dyno test on a 496 horsepower chubby, {yes, I know -- but we can still get some useful info on this...} and they tested different cooling fans to see what kind of drag each different type has.
Check this out;
Alternator, no fan: 496 hp
Black Magic electric fan: 494 hp
Thermal clutch fan: 487 hp
Nonthermal clutch fan: 485 hp
Heavy duty thermal clutch fan: 476 hp
High performance flex fan: 476 hp
Stock four blade fan: 473 hp
Low profile flex fan: 466 hp
One piece plastic flex fan: 460 hp
OE replacement six blade rigid fan: 449 hp
They found the alternator alone, a 63 amp unit, only sucked 1 horsepower.