Lots of cars that have 2 have the 2nd incorporated to the air conditioning compressor circuit. I would always go for max CFM and minimum draw. But that’s me
I dont know how much engine you got , but 2 12'' fans with more cfm than that wouldnt cool my 440/505 in a my 68 fastback. Depends on how ur engine is built and how much heat it produces --------
One 16'' wouldnt either !