Background: my case has terrible ventilation at the front and as you will see, an intake fan doesn't really do much. I tried every configuration to find out what the best possible cooling would be under my circumstances. I don't own a hard drive, so perhaps my temperatures are a little cooler than they otherwise would be.
These are stock speeds with stock CPU cooling. The case fans are Zalman ZM-F1 Plus 80MM, which come with a noiseless adapter that lowers the speed of the fan by about 1000 RPM. I eventually settled on a single rear fan with noiseless adapter, but I may need to modify this in the summer when temperatures skyrocket.
Idle
both fans - 24.5ºC
rear fan - 24.5ºC
front fan - 25ºC
front fan, with noiseless adapter - 25.5ºC
rear fan, with noiseless adapter - 25.5ºC
no case fan - 25.5ºC
Load
both fans - 64ºC
rear fan - 65.5
front fan - 71.5ºC
front fan, with noiseless adapter - 71.5ºC
rear fan, with noiseless adapter - 68ºC
rear fan, noiseless, 3.5 bay open in front for more airflow - 67ºC
no case fan - 71.5ºC
Ambient temp - 17ºC
Edited to add: I have an Asus P8H67-PRO motherboard. When using SpeedFan, I notice a temperature indicator for CPU that starts around 90ºC and then drops with load. What's with this?