Interesting post. To give you some more inspiriation, I'd like to share my build again, which I already posted here about half a year ago. On the side, you can use a Noctua A15 PWM, the 140 mm fan with 120 mm mounting holes. It fits next to the U9S, and can spin at a bit lower rpm. In my build, I have a front-to-back airflow, with the 140 mm fan on the side as intake, and an additional Noctua A9 PWM 92 mm fan on the front as intake. As you can see in the pictures, it channels air over and under the GPU, driving the hot air out the back. I guess the reverse, back-to-front, would also work, but I think sucking in the air via the cutout in the front panel is more efficient than blowing hot air against the front panel. I think this might be the most efficient way to cool both a non-exhausting GPU and a CPU, but of course you lose the front panel I/O.
Thats quite a layout. Thanks for sharing. I will be reversing the air flow soon and see how it compares once I received extra rubber mounts. I think its a big question that needs answering here.