The 1866 MHz. DIMM situation on AMD processors is a little bit confusing.
Officially AMD does NOT guarantee that you can run more than 1x DIMMs @ 1866 MHz. on FX series CPUs. It actually depends on the number of DIMM slots on the mobo if they guarantee 1x or 2x DIMMs to work at 1866 MHz. There was an offical AMD chart on the website some place but I've searched and can not find it at the moment...
That being said, you are asking a LOT to run 4x DIMMs @ 1866 MHz. as these CPUs were not designed for this purpose. They might run stable @ 1866 MHz. with the right BIOS settings but they may also not. There is no guarantee that these will work even with different BIOS settings, but here is what I would suggest that you try:
Use the latest mobo BIOS for your mobo
set CPU NB to 1.35v
set HT voltage to 1.25v
set RAM voltage to 1.6v
Try the default timings of 9-10-9-27 but they probably will NOT work. You most likely will need slower/looser timings such as 10-11-10-30. The slower/looser timings will not hurt system performance as in the past so if slower works for 100% stability, use it.
Be advised that you may be just as happy with a 100% stable PC running the DDR3 @ 1600 MHz. because MANY tests have been conducted with real applications showing that 1600 MHz. DDR3 is NOT a system bottleneck for a typical desktop PC using a CPU. For desktop systems using an APU, faster DDR3 frequencies up to about 2133 MHz. do show some useful performance increases because the GPU needs the added bandwidth that a CPU alone does not.