i read all the responses, a few notes:
1 - i am running a Mountainmods U2-UFO case OPEN, so i don't need any case fans. once i got in the habit of running my cases open there is just no going back. i have a whole box of 120mm panaflo fans that i no longer have use for since i started running cases open.
HERE IS THE PICTURE: http://farm9.staticflickr.com/8359/8321263198_587ec2de98_b.jpg
2 - i am really liking Thermalright Macho suggestion ! i was thinking - i should probably get Macho 120 since i want less noise, rather than more cooling ?
3 - i tried researching just now the difference between PWM and voltage control and didn't really understand anything even though i have electrical engineering degree LOL. i mean i know what pulse width modulation is, i just don't understand what difference it makes for the fan, compared to voltage regulation which is probably accomplished by pulse width modulation anyway, just in the motherboard ...
4 - if i went with lets say Macho 120 could i buy an even quieter fan to use with it ? what's the absolute quietest fan i could use there ? i don't really want to go passive as i will also be doing video editing on that computer working with files as big as 10 gigabytes.
5 - maybe i could simply unplug the fan while recording and then plug it back in when editing videos ? i still think 120mm fan would be enough as i would not overclock ?
i also have to upgrade my power supply to a silent one, but i will make a separate thread in power supply subforum for that.
PS: regarding the stock fan cooler - i certainly plugged it into the right socket - it says CPUFAN where it's plugged in. on the other hand i did not go into any BIOS settings for fan.
PS2: i have "ripjaws" ram that looks like this:
http://cdn0.mos.techradar.futurecdn.net///Review%20images/PC%20Format/PCF%20252/PCF252.wired_flow.ram-380-75.jpg so i don't know whether this might affect mounting with some coolers.