Clutch fan options on my 340?

Why is there always a issue, either there is a miscommunication or im not getting the premise on the correct setup. One thread shows the 70-71 dodge part list and under dart shows the 340 to have a 7 blade, then you state a 5 blade is reccomended, im just trying to learn the difference between the two and what is the best option for both availability and functionality with a fan clutch, i have no problem running the fixed fan but i figure if i can free up 10 hp or more it would be worth the time spent trying to learn about the setups with fan and clutch lol