If I know the stock rpm and cfm of a fan then I turn it down to say 1/2 rmp with a rheostat will the cfm also be half of the stock cfm or is there some other formula to use? I ask because I'm trying to find a good speed to run my Delta 50 db fan so its about 30-40 db but I also dont want to sacrifice more then 5 or 6*C. Motherboard monitor tells me the RPM and I would like to know the cfm of the fan. I want to see if a 80 cmf fan tuned down to 30 cfm is quieter then a fan that is ment to be run at 30 cfm in the first place. Any help would be appreciated! Thanks in advance.