^ Also, if you plan on doing a push-pull setup try to get as close of an rpm to the stock fan on the Hyper 212+ as possible. Too slow and you'll mess up the push-pull and probably get slightly higher temps than if they were close to the same rpms. Oh what I mean is the RPM/CFM should almost be the same as the Hyper 212+'s stock fan.
FYI, maximumpc did a test on the CM 212+ with two fans and saw very little increase in cooling. I have the same cooler and saw the same results. In fact using a slower RPM fan did improve temps a bit while a faster one actually increased them.
My personal recommendation, the cooler is great as is with one fan and the second is just not worth it.