The weight of the fan is only a factor when changing the speed of the fan. When a fan is up to a given speed it is the pitch and area of the blades that determines the power to move the air. The same fan, running at the same RPM will require the same horsepower to run regardless of engine size.Sure, send me the link...we will see if they actually post up the dyno results on screen with the fan being the only difference between runs.
P.S. I am sure the fan DOES care what engine its stealing power from...a 460 has a LOT more rotating mass than a 289...it will be much more sensitive to reductions in that weight at 5000RPM
Here is one with a clutch fan vs electric:
A whopping 3HP gain...true...a fixed fan will be a bigger gain, still looking for one. I dont consider engine masters(or any other magazine) a reliable source for any data simply because they all try to sell their advertisers products. Its far better when you can find individual before and after dyno graphs.
That being said, there are plenty of reasons to go to an electric fan over a mechanical one...from space, to better looking, to better cooling and anything else you can imagine.