Update: The store reversed the final-sale policy and I got the Sapphire Toxic Air-Cooled 6900 XT. Plug & Play it just worked.
No boot loops ...... except .... (and now onto the RAM)
The Samsung RAM works flawless. Mind you, it's 2666 and it's only 16 GB of RAM.
Before it's asked, all 128 GB of RAM worked fine for about 2 years before this nonsense started. So I know it's compatible with my Asus X299 Sage/10G
If I try any combination of Corsair (the 8 sticks of 16 GB I have) - it crashes at random. XMP will boot loop so that's a no-go. Manual or auto down to 2133, doesn't make a difference. Nor does the combination or slot. I CAN get all the sticks to recognize and post into the BIOS w/ XMP off (which was an upgrade before I replaced the GPU) - but I hardly can imagine all 8 sticks are bad.
So now, it's either memory controller on the processor, or the board. Both are still under warranty. Luckily, I actually have extended warranty on top of the manufacturer warranty for the 10980XE - and my ASUS warranty runs out in October, so I have time. If I have to RMA the board, ASUS is about an hour away from me and I can drive it there which is awesome.
If I have to RMA the processor, I have a 9900X I can use a backup.
If it's RAM, lifetime warranty, I'm good there, but given everything so far, I'm doubting it's these sticks.
If it's all the things, well s**t - I'll use my Macbook for a few weeks
Like I said in the post above, I tried 2 sticks of Kingston 3600 and that was a disaster no matter how I configured it. Could this be a memory controller failure I'm feeling? On a sidenote, FCPX (even w/ 16 GB of RAM) is SOOOOO much faster w/ this card. The machine is stable with it and the Samsung RAM - but I paid for the Corsair and have it and REALLY want to use it (I edit music videos, the waveforms take forever to load on such low RAM, this is painful)
BUT, the boot loops are gone with the Samsung RAM which is awesome and a good first start. Not to mention I can at least post and start the OS initialization w/ the Corsair at the lowest settings, but it either reboots at random before it gets to the desktop, or it gets to the desktop, but don't even think of exporting a video in FCPX - because it will reboot. The Samsung RAM was able to export a 25 minute 4K export without rendering first and it ran flawless. The Corsair with even 1 stick (I tried all 8 in different slots, it's been a long night) will barely start the render before I see the BIOS screen immediately.
Any insight on this would be super-appreciated. Thank you for reading this far lol