Andreas: next time you try 4 amd cards maybe it might be worth investigating the use of pcie x16 extenders. http://linitx.com/product/pci-expres...extender/10538

back when the gx2 was king I tried this with a reasonable degree of success ....those did vent all to outside the case though

Lifting alternate cards allowed fans to get more air.

I wonder if they make a 1u version?