First of all, don't have that exhaust fan pulling air out the back of the case, as this will create a vaccum between the heatsink and the fan, and you dont want that.
From personal experience, you should use the 80mm fan bay at the back to suck in air and blow it directly on the heatsink.
Using a cheap 16 dollar heatsink and some manila folder paper, along with an 80mm fan, i was able to clock a jiuhb 1700 t-bred to 2250Mhz, rock-stable, at only 43ºC.
You can also use the fan at the front to pull the air in, but i just used the side-case fan pointing out to pull heat out (and boy did it. outside case temps, along with room temps went up when i stressed the system).
Plan it right, and with a good heatsink and fan, you could go really high on air.
