First you should find out if your temps are due to high case temps or an insufficient CPU heatsink. Easy way of doing this is to monitor the temp at idle and then when stressed (run a benchmark for 10-15 minutes and record the peak temp).
Next take the cover off the case and repeat the tests. If you have a large temp difference, you have airflow issues in the case. A while back I read Intels temperature management recommendations and they say to suck air in at the bottom front of the case, and then exhaust it through the power supply.
Here’s an important point: Many power supplies suck air IN, not out. So now you have a situation where room temp air is sucked into the PSU, heated up and then pumped into the case. Then you have your second fan trying to pump more air into the case. Not good.
My Antec PSU did this. I took the cover off the PSU and turned the fan around. This alone dropped my CPU temp 4C.
/Markus