for passive, use alu.
for active, use copper.

both works better with some airflow,
alu : doesnt need/affected much by stronger airflow. having is enuff.
copper : better airflow = better performance. go as strong as u can.

personal experience = forgot to connect hsf power cable, crash pc after 2mins, with temps reaching 80degree+ when using jet4(full copper). never crashed with intel stock(full alu) when forgot to connect fan's power, just turtled..