H8DGT-HIBQF has 2DPC (2 DIMM per channel) design support. According to the design guidance from AMD, only 1DPC (1 DIMM per channel) MB design can support 1866MHz memory. http://www.supermicro.com/Aplus/support/resources/memory/display.cfm?mspd=1.866&mtyp=61&id=83A5A9893A3094EEFC15667E13447576