I have a built 400 and had cooling issues.
Tried the 7 blade clutch fan, then the 4 blade fixed, then 5 blade flex, then an electric fan (Lincoln MK5).
Also installed lower baffle/air dam, AC fillers, did the water pump mods (divider plates) and put in an aluminum radiator w/stock fan shroud.
After all said and done, I get the best cooling with the 5 blade stock flex fan. Temps stay around 185-190 unless I'm ideling for a while in 90+ degree weather then it will creep up to 200.
Just saying this setup work best for keeping my 400 cool and that I had tried many other options.