To get the G.Skill DDR4-4266 to work with the APEX, I had to do as Nate152 said plus ... I use manual rather than enabling XMP. Note that there is no DRAM ratio that will get to 4266 with Bclk at 100. That DRAM speed uses the 4133 ratio with Bclk at 103. One of the first things to back off if 4266 doesn't work is the blck - back to 100 and settle for 4133 speed.
I set DRAM voltage to 1.45 (should be safe up to 1.55), manually set the primary timings to XMP levels: tCL=19, tRCD=19, tRAS=39 and CR=2N and left the other timings AUTO. Mode 2 usually does a good job of conservative second and third timings that work right away. For higher bandwidth, you might try Mode 1, but that is for better overclocking at the expense of compatiblity.
I set DRAM voltage to 1.45 (should be safe up to 1.55), manually set the primary timings to XMP levels: tCL=19, tRCD=19, tRAS=39 and CR=2N and left the other timings AUTO. Mode 2 usually does a good job of conservative second and third timings that work right away. For higher bandwidth, you might try Mode 1, but that is for better overclocking at the expense of compatiblity.
I think 1.45v for DRAM would be safe. I would suggest raising system agent first to see if that improved stability, say 1.275v with 1.225Vccio.
DRAM voltage over 1.50 is likely safe, but not necessarily effective. Higher voltage has introduced memory errors in my experience. My 4266 kit works well up to 1.58V, but another slower kit throws errors above 1.51V. Voltage scaling is a variable thing with the Samsung B-die used on these DRAMs.
DRAM voltage over 1.50 is likely safe, but not necessarily effective. Higher voltage has introduced memory errors in my experience. My 4266 kit works well up to 1.58V, but another slower kit throws errors above 1.51V. Voltage scaling is a variable thing with the Samsung B-die used on these DRAMs.
The XMP setting lets BIOS and its presets take over, so yes a change in CPU profile goes with XMP. To get control of both CPU and DRAM, you have to manually override what BIOS does. Your choice is to go through the trial and error of many settings or settle for the easier, but not quite optimal outcome.
