Two fans only work better if the core is bigger than 20 x 24, otherwise a single 16 inch with a shroud tends to move more air across the face of the radiator.

As for CFM's, the 16 inch SPAL I have been using moves 3000 cfms, when you turn it on while holding it the thing will try to jump out of your hands.

Size 16" pull / Part# 2113*
[2113] $220.00
Size 16" pull / Part# 2113*

Part: 2113*
Size: 16" pull
Blade Type: Skewed
Thickness: 3.65
AMPS: 22.5
Airflow (CFM): 3000

Don