XMP profile has slowly become unstable over time. Is it the CPU or the RAM?

Sounds good to go with the CPU strap at 125. With all the trouble and testing you did it seems like something changed in the CPU over time.

I think you may be right. 2666@13-14-14-35 was fine for a few days and then today i had a blue screen followed by a scrambled bios again. i reset to optimized defaults and then re overclocked from scratch to my old cpu speed and set the memory to xmp and everything was fine for awhile. then i started getting issues like before even with xmp. right now i have it back down to 2400 and it seems ok. i don't think it's the ram though. i'll make sure it's stable for awhile an update the bios to see what happens. the thing that makes this confusing is i can run realbench stress test with 16gb enabled and it seems ok but i admit i didn't run it that long.

I find stress tests don't find hardware problems that well from what I see dally in the forums and on my rigs, they are good for testing overclocking. For me and what I see in the forums like the problems you are having only parts replacement works. I had to RMA skylake CPU for intermittent problems, then I had to RMA the memory on the rig I'm on now, it took me month to decided what part to try and RMA on both rigs, now everything is working perfect.

What do you mean by scrambled Bios?

"What do you mean by scrambled Bios?"

several times when i was experimenting with memory speeds i would try to restart (or it would just happen) and instead of going back into windows i would end up in the bios where everything was out of whack with wrong colors, things out of place, and the inability to effect anything. all i could do is power down completely and power up until i got a successful entry to the bios so i could change to more stable settings. are you pretty sure there's no way the motherboard could be an issue? when the ram is at 2400 everything is peachy but i already tried another set and it changes nothing so i returned it. that leaves the memory controller or the motherboard.

EDIT: If it happens again i'll take a pic and post it

Wow what you described sounds like a motherboard Bios problem, however the Bios uses the CPU and memory to boot up into Bios then boot the os. I would run it with 2400 speed for a while to see if you receive a BSOD.

If you had a motherboard Bios problem it would have trouble at stock settings.

2400mhz ram speed seems to take care of everything as far as i can tell but ill try it for awhile to make sure. im still not convinced that the motherboard is just traces between the cpu and memory and has nothing to do with ram stability. if that was the case they wouldn't have certified memory lists and bios updates to increase memory stability. i actually had sort of a similar issue on my last asus mobo and gskill memory but it didn't happen over time. it was like that from the start. asus swore that the ram was compatible with that model and they were developed together to work. i tried rma'ing the ram and it stayed the same. then i switched to mushkin blackiine and it was fine from then on. not really the same thing i know but that experience is part of why i hate throwing tons of warranties at a problem. it's too much work swapping things out over and over, costs me shipping, and costs an innocent company time and money.

To enable high performance Overclocking memory to work each motherboard manufacture changes Intel's CL memory timing and sub timings also Vccio Vccsa and ram voltage in Bios, so the Bios micro code programs the CPU memory controller with timings.

Example of Gigabyte XMP 3200 sub memory timings.
Intel's stock specification for timings. 2133 speed CL 15-15-15-36, sub timings 50-17-13-4-6-4-9-4-6-374-8-23-2.
Gigabytes specification for timings.---3200 speed CL 14-14-14-34, Sub timings 48-25-12-6-7-4-9-4-7-560-12-39-2.

3200 speed memory on Gigabyte.
Vccio Stock Intel 0.960v changed to 1.165v
Vccsa (System Agent) stock Intel 1.060v changed to 1.248v

Motherboard manufactures make a lot of Bios update changes to the memory sub timings and memory controller voltage (Vccio Vccsa) to try and have XMP overclocking memory stable. There is no Intel set standard for sub timings and Vccio Vccsa for overclocking memory otherwise all OC memory would work just fine like 2133 Speed specified memory.

interesting stuff. i'm gonna try 12-13-13-32@2400mhz for awhile and see how it goes. so far it's been ok for about 15 minutes and passed a short stress test. stil does about 41gb/sec bandwidth. not gonna complain. all the ram was about the same price and they say it doesn't matter much. it just bugs me that it was one way and now it's another. hopefully it won't get worse. ill try vccio/ccsa if this doesn't work.

One thing I forgot to mention once I was having memory trouble and I RMA'ed mushkin twice to get a good pair that would work perfect. Have you taken a look to see what Vccio and Vccsa is on your motherboard? If you have not you can use HWiNFO64 to see it.

couldn't find those settings in bios. might be called something else. this is with 2400 mem clocks at low latency and 1.35v dram voltage
EDIT: found the settings for vccio and vccsa. they don't show unless xmp is enabled. weird.

This is with XMP 3000mhz

Thanks for showing all your screenshots, I like to compare. The voltage is normal for that 3000 speed memory overclocked XMP. You could go a little higher with the VCCSA 1.208v and VCCIO 1.044.

no problem thanks for looking. kind of embarrassing that i couldn't find the settings for vccio and vccsa but it's not intuitive to have them come up only with xmp enabled. enabling xmp implies you want to click one thing and not worry about other settings. the settings should come up when you set to manual mode. funny thing is since i set it back to xmp it's been ok and i even reset a few times without overclock failure or being railroaded into a scrambled bios. i think going back and forth between manual and xmp settings crosses a few wires that need to shake out with a few power downs and restarts. this mobo is a little wacky. it tried to tell me i was turning the ram speed down from 3750mhz back to 3000mhz when i reset to xmp. the target values at the top of the settings screen isn't always accurate. there's also a decent chance i'm just in over my head and don't get it. either way thanks for the assistance. i'll see how long xmp 3000mhz holds up now that it seems ok again. if i get issues i'll bump up the system agent a little and see what happens. just out of curiouslity what are the cool kids using to measure overall cpu horsepower these days? i want to see what ram timings get the best score. is it still just 3dmark cpu score?

here's what happens with the bios sometimes at higher memory speeds. This particular one was in xmp mode.




And here's what it's supposed to look like

I see what you are taking about, something is not working correctly with overclocked memory. With my Gigabyte it wont even boot up with setting memory manually at 3200 Speed, I have to use XMP. Can you use XMP and manual? Did you have a problem with XMP mode to post the Screenshot.

Yes the messed up bios pic is in xmp mode. it happened when i was trying to change back to manual mode from xmp.

Did it happen when you rebooted to manual or just when it entered the Bios screen in XMP mode?

It happened when I restarted to change from xmp to manual.

You are having all kinds of fun, I am also, I was seeing if I could manual set 3200 speed without XMP and I tried everything even advanced sub timings, however there is a lot more timings that I'm not going to try I give up LOL, I can run XMP and play with memory speed, CL, voltage and it boots up fine. My motherboard also has quirk when I change the Vcore to manual and LLC then go back to my default DVID offset settings, I have to shut down the PC and reboot otherwise the Vcore is lower than what it should be.

From what you described I would run XMP if you have not tried that for a long period of time. XMP sets all the timings plus everything else, some motherboards when you increase the memory clock speed the auto configuration changes all the sub timings.

i think i need a hard bios reset. i tried xmp and started getting suggestions from windows that i try a repair install. gotta go to bed. this is wearing me out. maybe stock isn't so bad good luck with your situation. if i could help you i would have already helped myself. sorry.