[vettestr]

Mike,
I do not no Zirgo fan but have had great performance from Spal and the Black Magic from Flex-a lite. Many companies over rate the real world CFM rating or delivered CFM when flow is restricted by radiator and surface area etc... Check the amp demand against size and CFM to see if it falls in line with others as a sanity check.

I am a firm believer in more is better to make sure one of the major car systems won't leave you walking. Use appropriate wire gauge and a control relay to allow self cycling or on demand on/off control. The alternator is controlled by demand so HP loss is not a real concern in my book. A high flow or efficiency fan will simply cycle on/off quicker but is there when demand increases. The engine compartment also benefits from fan operation as heat is the big problem for many items and electronics.