Crossfire 4850 and 4870 Airflow Help

I recently threw in my old ATI 4850 into my wife's pc as a crossfire setup that already had a 4870. For the most part, this has worked great. I have have seen a decent improvement on all games played with very little issues. During periods of extended gameplay(3 hours+), I have had the cards overheat on me. I wanted to walk everyone through a basic setup of my fans on the machine to see if I am doing anything wrong here. Please consult the horrible sketches below to see my current airflow setup(not at home to take a picture):

Inetrior Side View of Case:
----------------|
|PSU-----------|
| --------------|
|1-CPU---------|
|---------------|
|---------------|
|-vcard1------2|
|-vcard2-------|
-----------------

#1 = 120mm Exhaust Fan
#2 = 120mm Supply Fan

External Side Door of Case:
----------------|
|---------------|
|---------------|
|---2-----------|
|---------------|
|---------------|
|---1-----------|
|---------------|
-----------------

#1 = 80mm Exhaust Fan
#2 = 80mm Exhaust Fan



Please note that the door sketch goes directly on top of the other sketch. In other words, the exterior fans mount directly on top of the video cards and the CPU. Should I have the exterior fan#1 on top of the video cards supplying air instead of exhausting? Should I also open up some of the blank PCI slots between the two cards to encourage more air to escape out the back of the case? Any advice would be great.

How narrow is the case?
I wonder if you just have too many sources/sinks for air and it's not keeping the flow clean... if there's too much mixing, it can be counter productive.

Since you have 2 exhausts at top near CPU and only 1 on video cards, air flow from the inlet at the front would want to go more towards CPU rather than the video cards... try turning off the case exhaust fan (or lower speed setting) at 120 mm exhaust fan to see if that helps... also keeping the areas where air flow occurs clean would help.