i use zirgo fans on the cars i build , i have not " tested " the cfm myself , but they do pull alot of air . i had a coustomer using a autoparts store brand straight blade 16 in fan on a 32 roadster with a 351 ford ( thats the first problem ) but i changed to a zirgo 16 ,and have had no problems since with heat .
i know a mechanical fan is better IF you can fit it into the car . my willys ,37fords with lt1 , nomad with ls1,and the 32 mentioned could not use a mech fan so i have to use electric . so would i recomend a zirgo fan , yes . along with a good shroud ,good relay power set-up ,thermostat and a good proper sized radiator .i can cool a 704 hp 540 in a willys with a small grill opening in 100degree weather .
good luck greg !