Hi, I'm Jewel with Kingston Technical Support and would like to extend our assistance. The default speed profile of the memory described, part number KHX21C11T3K2/8X, would be 1333Mhz which is what it runs at without changing settings to overclock. It's specification sheet can be found here:
http://www.kingston.com/datasheets/KHX21C11T3K2_8X.pdf . This memory has two XMP profiles to overclock to 1600Mhz and 2133Mhz speed. Since you have an AMD board you may not have the ability to select memory profiles for easy setup as XMP profiles are for Intel chipsets but some AMD chipsets do have a memory profile selector in the BIOS, if not you would need to set the memory timings manually. This memory is not set for 1866Mhz speed but as it can reach 2133Mhz it theoretically should have no issue running at 1866. There are a few ways to reach this speed, here are some timings that you can try:
DDR3-1866 CL9-11-9-27 @1.65V
DDR3-1866 CL11-11-11-27 @1.5V
DDR3-1866 CL10-10-10-27 @1.5V
Also, per your motherboard's manual it is best to have the memory installed in slots DIMM_A2 and DIMM_B2 (the blue slots) when only two modules are installed for best performance. This would be for Dual Channel performance and may help with stability when running at 1866, if you do not already have the modules installed in this configuration, it would be best to reseat them into those slots. I hope this helps, if you have any further questions or concerns, please call us at 1-800-435-0640 (USA and Canada only) M - F 6am - 6pm PT and I or another available Technician will assist you. Please be sure to have the part in question on hand when you call.
Thank you for selecting Kingston as your upgrade partner.