I do know that the Cummins I swapped in my K30 is easily cooled with an Advance Auto electric fan, although I do have a Taurus or Volvo fan (don't remember which one it is) to swap on it one day. Hell, the fan on that one rarely ever kicks on. It just has a stock, 1st Gen Dodge radiator in it. I think it'll get up around 190 if it sits still for a while, but with if the fan kicks on/any forward movement/raised RPM, it cools back down very quickly.
Over in the Duramax world, on the other hand, the only people who get away with electric fans are mostly dedicated race trucks or strictly highway drivers. I want to say I read a forum post by an actual GM engineer (who was also a Duramax enthusiast) that said the stock fan, with the clutch engaged) could move right at 10,000 cfm. I can only imagine what kind of power/fuel economy that robs, but it's interesting to think about having a 600+ hp fan on my truck. If they made some electric ones that'd handle the job and fit in the given area, I'd love to see how much more pep the truck has!
The rest of your points: very valid, no disagreement. This one though...do huwhatt?
That's what that little bi-metallic spring does
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That said, I do certainly prefer an electric fan myself. I did the 05+ truck fan swap on my 99 Silverado and they're pretty sweet.