Hey, I saw your reply on this thread: ASRock FM2A75M-ITX 5800K GPU locked at 400Mhz with 2133 memory
And I have to tell you this seems to be a general problem with ASRock motherboards and DDR3-2133 memory. Their support team hasn't gotten back to me on this issue. I have the FM2A75M-DGS instead of the -ITX, and it is suffering from the same problem even though it says under specifications: - Supports DDR3 2400+(OC)/2133(OC)/1866/1600/1333/1066 non-ECC, un-buffered memory (http://www.asrock.com/mb/AMD/FM2A75M-DGS/?cat=Specifications)
If you hear anything from ASRock, please let me know. And also please tell them this is happening with other motherboards too, like the DGS. I tested this problem with FurMark and GPU-Z.