Originally Posted by Omega
Now, here's how it should work.
Two air intakes on the bottom of the case. One under the GPU, one in the middle. The air from the GPU-bottom-case-intake will go up and through the spinning GPU fan which will thrust the air out of the case. the heat that isn't expelled backwards will rise up. The middle-bottom-case-intake will just blow up. That's it. Then put an exhaust on the top. Or two. Or three. All 12cm, of course.
For better CPU cooling, maybe re-engineer a slot cooler to go above the GPU slot and suck cool air in and push it up onto the CPU. Where the rear exhaust fan would go, make that an intake also. If you have a fan on the bottom of your PSU, leave it be. If you have fans on the front and back, make them blow into the case, maybe through their own thermal duct.
Then have one more intake on the front of the case, in front of the hard drives. This will blow cool air over the HD's, then the airflow will hit the upward stream and out the top of the case.