I cannot get behind that fan clutch discussion

[BillyDeluxe]

Hi folks,
my 65 has a bored 350 and a overheating problem. Especially during the summer month when I get into high traffic.

I am working since quite a long time to get it fixed. I switched the radiator to an original Harrison which I bought from the States. I played a little bit with the rate of cooling fluid. I also bought an original Shroud but unfortunatelly it does not fit anymore as my engine and drivetrain is a mixture of Blazer rear end and 80s C10 truck engine (don't know where there 350 tranny is from). So all slipped a little bit forward and there is not enough space anymore for the shroud.

My actual idea is to rework the radiator with a high performance net and to switch to a clutch fan instead of the 19" fixed one what I have now.
I read much about clutch fans and advantages and disadvantages but I really cannot get behind it so I ask for your help.

A clutch fan operates at a lower speed than the shaft when its disengaged. As soon as it engages it works on a speed of 60%-90% of the shaft depending on the clutch (Thermal/heavy duty/severe duty). But all in all it work slower than the shaft, right?
Okay I agree that it frees a certain level of horse power but I am sure it's not that much.

So why switching to a clutch fan when it's slower than the fixed one (apart from the horse power topic)?

Can anybody give me guidance here?