Well, the exhaust fan or fans of the case are the most important ones. Such a fan will see to that the air is dragged thru the box and out as fast as possible. The problem with your case are that the 80 mm exhaust fan is quite small and will have to spin very fast and therefore will be noisy at the same time to be able to make the air get out in a decent way. It would have been a lot better if that fan had been at least a 120 mm.
The RPM is'nt the important thing here. It's the amount of air the fan can push = CFM = Cubic Foot per Meter. The higher CFM the better. The lower rpm and at the same time higher CFM a fan have? The better. More RPM, often mean that the fan will be noisier.
One thing you can do to help the 80 mm fan, is to dismount it, and then tape up a strudy little bag securely over the fan hole on the inside of the case. Then take out a plier and snip away the rear case fan grille. The bag vill prevent any metal shards or dust to get in contact with the hardware wich is dangerous for it.
That grille, acts like an "air brake" and makes the hot air bounce back and forth between the fan blades and the grille before it gets out. Removing that grille will also make the fan a bit less noiser.
There are fan adapters / funnels that allows you to to mount a 120 mm fan to an 80 mm fan mount on the outside of the case.
Here are a couple of fan suggestions:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835608006 This is likely the most silent and at the same time the most efficient one.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835352009
The 120mm fan with this adapter.
http://www.newegg.com/Product/Produ...6022&cm_re=Fan_adapter-_-11-996-022-_-Product
The case fans have a small arrow on the edge of the housing wich tells you in wich direction it will blow.