I'm just going to leave this here....
Sabrent Rocket 500GB PCI-E 4.0 WORKING @ 4.0 on CH6.
Every second since my initial post, this SSD has been functioning well, with no issues at all. I have been playing Borderlands 3 on it the entire time to make sure it wasn't going to crash or give performance issues.
So.... I am personally at a loss. Asus Crosshair VI Hero PCI-E 4.0 IS working for me. There is an option for the X16 link to use PCI-E 4.0 mode too.
Now, I am not just outright saying that "YES!! Gen4 works with CH6/X370 ABSOLUTELY!! Completely compatible!!!". So far, there hasn't been the slightest issue. Seemingly. Gaming and benchmarks come back positive. That's not enough for me to make a final judgement however. We need to do something like PC Mark or something along those lines to really test the drive "real world" and compare it with same drive & an X570 chipset board. Sustained writes for more than "X" amount of seconds may suffer, possibly other weird errata.
I do believe however, in the end, there will NOT be any issues with this board specifically. It is a FANTASTICALLY made motherboard. I have had a Ryzen 1700 @ 4.0ghz in this, a Ryzen 2700x @ 4.3ghz in this, and now.... A Ryzen 3600 @ 4.2ghz using PCI-E 4.0 when it was never supposed to do so. I personally have absolutely no choice but to say this is the best board I have ever owned. Period.
The PCI-E 4.0 issues, as I understand them, arise when the copper traces within the motherboard are not up to the task of doing PCI-E 4.0. That, AND, the physical routing of said traces. For all intents and purposes, the designers of this board went overkill with size of the traces, or copper purity, or something to make them top notch. Routed the best way possible, the fact that the m.2 slot is decently far from the CPU and this still works.... REALLY says something. I have Borderlands 3 on the new Gen4 SSD and nothing else. The game actually almost plays perfectly now. I am one of many having stuttering issues. Before the game was on a Samsung SM951, no slouch. Still, the drive difference is noticeable in game. It's smooth 98% of the time. IMO, if there was an issue with the SSD @ Gen4 on my CH6.... I certainly wouldn't get better perfs, or one would think anyway. The fact that m.2 works from so far away from the CPU, means IMO, the x16 slot will probably work in Gen4 mode too.
I do REALLY wish WE could have our cake and eat it too, however, BIOS 7201 I believe is the last BIOS to support Gen4 testing. The AGESA is at 18.104.22.168 I believe.... so it could be better. I was hoping those, or some modded BIOSes floating around would have had the Gen4 enabled BIOS used as a base. No one answered me, not once, or anyone else about the BIOSes themselves or Gen4 support in general for the CH6. I am not complaining, I just find it hard to believe I am the first one to try this on OCN. Let alone, honestly, this thread. LOL.
Cheers guys, any thoughts welcome!