Thank you for your answers.
I regret buying all these expensive components without deeper knowledge.
I first assembled my first PC when I was 16, back in 1996. Things were much less complicated back then.
After wasting money on a custom water cooling loop which I was not able to mount (due to missing pices and bits the seller did not send me...NEVER buy second hand PC parts!), I settled for the best air cooling solution...just to find out I made another wrong choice.
Now, I would like to solve this issue without spending one more penny. Here is the list of components I bought so far:
http://uk.pcpartpicker.com/p/mrP9ycI am attaching 2 pictures to show you the orientation of the fan/radiators, the position of the RAM modules (Corsair Diamond Platinum, which unfortunately also create a hindrance to the Noctua cooler) and the GPU.
I trusted pcpartpicker when purchasing the components for my build and nothing about this incompatibility was mentioned.
So, I have attached the card to the 8x slot. Reading the mainboard manual I found out that all the PCI-E slots are 16x, but running - respectively - at 16x, 8x, 4x and 4x. When the 8x slot is populated, the 16x will run at 8x.When one of the 4x slots is populated, the 16x will run at 8x and the 8x will run at 4x.
I really do not understand what the multiply factor means (bandwidth?), but I hope that mounting the GPU card in the 8x slot won't dramatically affect its performance.
I am afraid it is the only choice I have...I don't want to buy AGAIN another component to cool down my CPU.
Another solution would be to unmount the RAM modules radiators and replace them with low profile ones, so I could change the orientation of the CPU radiator/fan...and try to use the 16x PCI-E slot...
Any suggestions?