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I'm hopeful that Henry will help us with some empirical data about head temps. Another Pelican asked what the CHT limit should be, but I believe RoninLB is currently on the road and may not have his log of CHT data handy.

There are a few different dimensions to the cooling issue. First, our engines are air and oil cooled, with oil cooling the pistons (for those cases which have squirters installed) and providing cooling along with lubrication to the valvetrain and other moving parts. Air plays a role in cooling the cylinders and heads. And importantly, air plays an important role for cars with an engine-mounted cooler, insofar as airflow through the cooler is critical to maintaining low oil temperature.

The fact that the 911's cylinder head is a much better design than the 356/912 or VW head does not obviate the need for air cooling, which is why Henry said, and I hope I am quoting him correctly, and I agree, that it's critical to monitor head temperatures if you reduce the drive ratio to the fan.

It's like the three little bears: you want it JUST RIGHT, just enough airflow to maintain CHTs in an acceptable range, while maintaining oil pressure between 180 and 210F or thereabouts. More may help from a longevity standpoint but it costs horsepower to drive the fan.