Biggest single you can fit will always pull(or blow)more air than any duals you can fit in.
I run a 16" puller and a 16" blower either side of my 440 barracuda.
Not always true. I fit four 10" fans on my rad. Combined they have over 4000 cfm capacity and cover nearly all of the radiator core. This is more efficient in terms of cooling and can be less demanding on the charging system. They are wired independent of each other and can be turned on as needed.
