honestly, I would recommend not even getting an 80 mm fan. The 80mm Tornado fan is not worth even owning it makes so much noise. Trust me, I used to own it and I never got used to it being so loud.
Instead, I just bought an 80 to 120mm adapter so I can place a 120mm fan where an 80mm would usually fit. The fan I got for it pulls about 80 cfm and is more than 20 dba's quieter than the Tornado. Just make sure that a 120mm fan won't interfer with your motherboard and other components.
Coolerguys.com has a good selection of cheap adapters.
Also, punching a hole in the top of my case and attaching an exhaust fan has helped my heat tremendously.
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