Thanks for the detailed answer. I have finished the build in a different way though.
During gaming I found the temperatures to be a tad bit high, so I added a 40mm noiseblocker fan to the side of the enclosure.
The noiseblocker fan turned out to be quite noisy (duh) withouth pwm at max rpm 12v, so I added a fan speed reduction cable which reduces the voltage with a capacitor to 6.5v or about 55% fan speed. Much better. The fan is connected in the following way: Floppy to molex (pe4l supplied) > molex to 2p fan > 2p fan reduction cable > fan, as you can see in the pic below:
I made a cover plate from the bottom of an old 3,5" hdd enclosure I had lying around and ripped the cables together:
I sleeved the cables, and the end result:
Btw, thanks NANDO4 for your amazing thread, withouth it I wouldn't have started building an egpu.