So I've overclocked my i7 to 3.5ghz and I have the Scythe Mugen 2 which is doing a pretty good job. My temps idle at about 40 C (I have a C0), but I'm thinking about upgrading the my case cooling. Currently I only have stock fans in my case (CM 690) and I'm trying to decide if I should by more fans for my case or just replace the current fans with fans that push more air. Currently I've got three Cooler Master fans that push about 50 CFM. So should I just by some more Cooler master fans and a fan controller or should I upgrade to better fans?
I usually add fans before I buy faster ones, for noise concerns. I would start by putting a fan in the empty slot on the side panel (I think it's over the CPU?). This should help some with your CPU temps. Then I might add an exhaust on the top.
Don't expect huge gains here though, your case already has very good airflow.
Sole purpose of fan controller is being able to lower your fan speeds when you are not doing CPU/GPU intensive stuff to keep it quiet and then crank them up when you need the extra cooling.
If you don't care about the noise, I don't think you need a fan controller. If you get some fans and think they are too loud, you can always add a fan controller later.
Also, I wasn't recommending a fan for behind the mobo, that seems sort of pointless to me. I was recommending a second one of the left side of the case, where there was already one pre-installed (at least from what I can tell of reviews of the case online, I don't own one personally).