majax; what is the goal here?
the fans on the hyper212 aren't bad, and by adding a second you'll only see 1c to mayb 4c difference in temps. what are your current temps and what is your current system? The hyper is a good cooler, but it is limited in upgrade and performance as it is an entry level cooler in comparison to other tower/heatpipe coolers.
do to the gaps around the fan and fan shroud there is a lot of wasted air blown around the hyper212. have you considered mayb a foil tape to block off these gaps and FORCE all the air through the hyper212? mayb play with that and see what temp improvements you get. for that matter, what thermal paste are you using?