Does high CFM and RPM make a difference?
Well, depends. But cfm is important and RPM is best ignored. Depending on the overall airflow layout of the hardware inside the case, some cases are better with high cfm (especially in a mid tower where there's obstruction in the upper section, around the heatsink). Lower cfm does the job for case fans, higher cfm does good work for getting the heat away from the heatpipes of the heatsink.
This is what one has to keep in their mind:
# More fans does not mean better/quicker airflow: Putting more fans would either lead to negative airflow (either pushing the fresh air out as soon as it comes in or pushing out air where there's not enough fresh air coming in) or no effect at all, therefore power is getting wasted for no reason at all. This funda applies for hsf's push-pull configuration. Only few heatsinks have shown improvement in push-pull configuration. AFAIK, true120e rev C is one, my cooler is another.
# Positive airflow can be achieved with low cfm or high cfm. For a mid tower case, couple of low cfm connected via molex and for aftermarket heatsinks, medium-to-high cfm fans will suffice. Whether the temperature will fall when the heatsink is facing up or the rear of the case depends largely on the overall airflow, so one will end up doing RnD on their system.
I am confused because I have this CM 90CFM 120MM LED fan which I got for 450bucks for HDD's.
The ones who got with the case?
Someone on TE said that the CM fans are bad for heatsinks as they don't create much air pressure. So how do I know that a certain fan is good or bad?
cm fans are bad choice for installing on the aftermarket heatsink, especially when the VCORE is bumped. For case? Yeah they should do well with stock-to-mild oced systems with max mid range graphics card consuming around 170wish on load- till they start making noise. I wouldn't call it the problem of the CM fans necessarily. They are also ball bearing at the end of the day. Antec 900's case fans are good. I have couple of them lying around, alongwith the xigmatek's fan.
How do you know if its good for bad? RnD!! Either that or take a word of a neutral person who is technically sound. This is the reason we need people to be unbiased and give honest opinions or else people genuinely interested either will be obliged by taking advice from a foreign tech forum or being victimized by buying technically inferior product because of n00b's advice.
@ maverick: Check at primeabgb.com or lynx-india.com, one of them should have it.