I was on the fence about upgrading from my H60 push/pull to reach 4.5Ghz without going over 75c. Well I officially am Oced to 4.5Ghz with a H60 in push/pull!
I used a generic 120mm fan with 79.x cfm as my second fan. This however wasn't working alone. So I cleaned off the cpu and H60 plate and applied artic silver 5. I also had some thin rubber sheets laying around so I used a 120mm fan to make a template of it on the rubber sheet. I made two gaskets that made it so the air couldn't leak from between the rad and fans. These two steps worked for me.
After 30m of prime95-64bit version my temps on realtemp 3.70 are 70c/73c/72c/66c. I decided 30m was enough as I kept seeing the temp peak at 73c and then drop to 71c. It should also be noted my house is kept at 73f with 50% humidity.
My case has two 120mm 79.x cfm fans intake in front, two exhaust with rad, and 140mm intake on top (unknown cfm)