This link should give you an great idea of the electric fan you should be using.
http://flex-a-lite-blog.com/2010/04/...-electric-fan/
Pretty much say's for a v-8 it should be at least 2500 CFM's, a puller, and cover at least 70% of the radiator. Of course, with more HP the more CFM's you should run.
I definitely would not run to small of a fan set up (whether it is CFM or Coverage). You may cool the engine, but keeping the transmission cool is another story. I was figuring these things out myself after getting my truck together, I put a dual fan setup on mine from the salvage yard, covers about half of the radiator or a little less. Fluid started coming out the dipstick tube of the transmission. Found out my issue after I did the research. Not enough CFM or coverage of the radiator.
Hope this helps.