IMO the plastic Ford fan is better balanced and much lighter than the metal Jeep fan. If anything WP life should be improved with the Ford fan.
A fan clutch is designed to limit the fans speed. So WP pulley size won't effect the top speed of the fan. On a ford this may be 3000 engine rpm and with a smaller pulley it may reach maximum speed at a lower engine rpm but terminal fan speed will be the same...........With a properly working fan clutch.
I hope this makes sense.The fan will reach top speed sooner but won't be spinning any faster regardless of pully size because the fan clutch won't let it spin any faster.
As for the cracks in the Ford fan blades. I got mine just too see how it worked and it was only $8 @ PicAPart with cracks. But in all my years working in the automotive cooling industry I have never seen a Ford fan split where the plastic is molded onto the metal hub.
The plastic WP impeller is an entirely different kind of Plastic than what the fan blade is made from and the WP impeller is in extreemly hot coolant and under pressure. The Radiator fan just pulls air through the Radiator and Condenser.
It's life is easy vs an impellers life.
Don't take me wrong here I'm not trying to start a fight----> I think that your over thinking the plastic fan thing a little. If you want to build metal 7 blade fans for Jeeps that great! But untill you do were stuck with few options if somebody wants to upgrade their fan.
My Jeep has always ran hot. I've done lots of changes and each improves it a little. From hogging out the thermostat housing to bolting the stock fan clutch solid, different Radiators etc.
Even the bolted fan clutch allowed the engine to reach 235* on a 105 degree day with the 5 blade fan.
I saw 207* last week when it was 105*. I have not noticed any decrease in MPG. Infact I think it went up a little but thats a given when going from a bolted fan clutch to one that works.
Now that quite a few ppl are trying my fan idea time will tell but I think that Ford builds a more efficient fan blade than Jeep does.