Here is a partial view of the Flexalite 15in S/S flex fan.
I have never been one to trust my engine's life to an electric fan...have seen too many motors cooked because the electric fan system failed. Clutch type, aka thermostatically controlled viscous fluid-, fans are quieter than a flexfan; but are inferior in performance. It is designed to be less efficient in moving air in order to achieve 'quiet' operation. At best, a clutch type fan provides marginal air flow; and clutch type fans diminish in performance as the miles accumulate.
I am not interested in "marginal" cooling capabilities. With a boosted, intercooled, air conditioning equipped motor, marginal doesn't cut it. Nor does the intermittent cooling provided by an electric fan.
For the SP motor, I converted from clutch type to S/S flex. I kept the auxiliary electric pusher fan up front; and it is still correctly hooked up and wired in. I doubt that it will see much duty; but it is there if needed.
The Flexalite fan is rated to 10,000rpm. And it pulls a LOT more air through the radiator, the intercooler, and the a/c condenser; especially below 2500rpm. It is the best way to go to insure adequate and reliable air flow. I have them on ALL my vehicles; and on many of my customers' as well.
UPDATE: I love my Flexalite fans. They perform very well. But they do not last forever. I have run some of them for over 200,000 miles. And I have had to replace a couple after less than 50,000 miles. The blades DO flex. Which means that the metal can and WILL fatigue over time. The more aggressive the driving style, the more stress and flex the blades will see.
The bottom line is this: the flex fan will do a very good job; it will do its job until the blades fatigue. The fans have to be inspected periodically. And it will have to be replaced some time. The rule of thumb I use is 5 years/100,000 miles; with at least an annual close inspection of each of the blades on the fan. Any evidence of fatigue results in replacement. And when the fan reaches either 5 years of age or 100,000 miles, I usually replace it as a preventive measure.
For some of my customers who like to drive more aggressively, and at higher RPMs than a mature adult would normally drive at, those fans are checked more often. And they do end up being replaced more often.