Sometimes it's hard to improve on what a car manufacturer, with all their money and resources, installs as stock on their vehicles.
Several years ago, a friend of mine, who's a big deal in the Sunbeam sportscar club, did an experiment, trying several different cooling fan setups on a Sunbeam Tiger. The Tiger, powered by a small-block Ford V8, is known for it's marginal cooling system.
He found that the performance of some aftermarket electric cooling fans suffered from their typical installation up against the radiator core, when they actually worked better if they were spaced away from the radiator about half an inch or so.
Among all the different fans tested, including push and puller electrics, and a variety of aftermaket fiberglass and flex-steel pump-mounted fans, the primitive-looking four-blade stamped-steel stock Ford fan was hard to beat.

Happy Motoring, Mark

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DrDKW

I know this is a long-dormant thread, but I just wanted to add my recent observations. I have a 1982 300D (turbo), and a 1983 240d donor car. The 300D viscous-coupled metal fan has wider and more steeply pitched blades, so it is clearly designed to move a greater volume of air at any given rpm than the plastic non-clutch fan of the 240D. The 300D also has a larger fan pulley, so it turns more slowly at any given engine speed. I decided to try the plastic direct-drive fan in place of the metal fan and clutch in my 300D. I deleted my A/C, and it's electric fan, so I wouldn't recommend this for air conditioned 300D's. I find the plastic fan to be quieter, since it has less blade pitch and smaller blades - this difference is subtle, and most noticeable at idle. I also see a bit more temperature rise at idle, but nothing alarming, and it quickly drops back to normal (80°C) above 25 mph. I prefer the simplicity and lighter weight of the plastic fan, so I will be leaving it.