Correct, two measures for fans are CFM (volume of air moved) and static pressure (how strong it can pull air through the radiator). A fan with high cfm in the air might not have high cfm behind your radiator. RPM just tells you how fast the fan spins, without anymore info it's impossible to tell if it's a good fan or not.

Car companies spend millions daily to research cooling efficiency, if there is a better solution, it's them who'll introduce it, not some small fan company. Your high cfm fan at low speed can even restrict flow through the radiators at high speed.

while I have free time at Ipoh, I actually wrap the piping.

somehow or other, I actually felt the air con is much cooler.

could it be a placebo effect or really a fact