PhantomApollyon
Thank you to everyone for the feedback so far, I tend to agree that my #1 is/was largely just a Windows HDR quirk as suggested and am largely writing that off for now. (though I NEVER experienced this with my 2080ti FTW3 Ultra)
 
My main outstanding concern now is an issue with getting no video output at all from the PC from a cold boot until after some undetermined amount of time, EXCEPT the initial BIOS splash screen. I want to front load this with the fact that I NEVER experienced this with my 2080ti FTW3 Ultra and beyond the GPU/drivers, nothing else has changeg with the system.
 
Generally the delay in video output will be anywhere between 30s-120s, with seemingly no real rhyme or reason as to why it starts working. When it does start working, I'll be at the Windows 10 desktop. What's interesting to me is that it always shows the BIOS splash screen just fine (not HDR), and once it starts to boot into Windows, the signal cuts out and the TV shows no signal though it does recognize that something is plugged into the HDMI port if you look at the input window. While doing some testing this morning I actually had a white VGA error light on the board show up after waiting ~2minutes for video to display, and when I was walking over to look at the LED the screen lit up without me touching anything at all. I did a power cycle and the VGA light was gone and things are working normally again. It's almost like something's odd with the HDMI handshake as it attempts to boot into Windows, which triggers HDR. 
 
Any thoughts on this one?

Try a different/shorter cable is the best advice that I can give.
 
I started getting random flickering with my Zeskit after it had been working for some time (4K 120Hz 10 bit RGB full w/ HDR and Gsync on). Figured out that it was EMI from the GPU / PSU and re-routed it further away and added EMI chokes. But I'd still (though rarely) get that random flickering. That all went away when I got a 6 foot cable instead of that 10 foot, thicker & now EMI choked Zeskit.

arestavo

PhantomApollyon
Thank you to everyone for the feedback so far, I tend to agree that my #1 is/was largely just a Windows HDR quirk as suggested and am largely writing that off for now. (though I NEVER experienced this with my 2080ti FTW3 Ultra)
 
My main outstanding concern now is an issue with getting no video output at all from the PC from a cold boot until after some undetermined amount of time, EXCEPT the initial BIOS splash screen. I want to front load this with the fact that I NEVER experienced this with my 2080ti FTW3 Ultra and beyond the GPU/drivers, nothing else has changeg with the system.
 
Generally the delay in video output will be anywhere between 30s-120s, with seemingly no real rhyme or reason as to why it starts working. When it does start working, I'll be at the Windows 10 desktop. What's interesting to me is that it always shows the BIOS splash screen just fine (not HDR), and once it starts to boot into Windows, the signal cuts out and the TV shows no signal though it does recognize that something is plugged into the HDMI port if you look at the input window. While doing some testing this morning I actually had a white VGA error light on the board show up after waiting ~2minutes for video to display, and when I was walking over to look at the LED the screen lit up without me touching anything at all. I did a power cycle and the VGA light was gone and things are working normally again. It's almost like something's odd with the HDMI handshake as it attempts to boot into Windows, which triggers HDR. 
 
Any thoughts on this one?

Try a different/shorter cable is the best advice that I can give.
 
I started getting random flickering with my Zeskit after it had been working for some time (4K 120Hz 10 bit RGB full w/ HDR and Gsync on). Figured out that it was EMI from the GPU / PSU and re-routed it further away and added EMI chokes. But I'd still (though rarely) get that random flickering. That all went away when I got a 6 foot cable instead of that 10 foot, thicker & now EMI choked Zeskit.

Appreciate the input. I will do some more testing with the Monoprice 6ft cable tonight to see if I can reproduce it on that cable.

Update: I tried the Monoprice 6ft cable with no change in behavior at all - still having the same issue

PhantomApollyon
Update: I tried the Monoprice 6ft cable with no change in behavior at all - still having the same issue

Start a new thread / get ahold of EVGA tech support: https://www.evga.com/about/contactus/
 
(and make sure you're running the 3.11.25 firmware on your CX)

• AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable --- Confirmed no problem, 4k @ 120, 10bit, G-sync, 4:4:4

So I picked up my CX 48 at Best Buy yesterday and got an AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable have had no issues with my 3090 ftw3. First thing I did was upgrade my firmware to 3.11.25. Any of the AudioQuest 8d-10k listed cables at Best Buy should be fine but anything over Pearl gets expensive quick and you only gain better auto quality apparently.
 
Edit: Woops restrictions on new members and links...sigh. Tried to post links to the cables. Just search for the Pearl or Ocean (apparently same quality as Pearl but BestBuy exclusive) 8k-10k HDMI Cables at BestBuy. Also AudioQuest has their own site as well if you want to see more info on the cables.
 
 

PhantomApollyon
Update: I tried the Monoprice 6ft cable with no change in behavior at all - still having the same issue

I just read that someone else fixed a black screen problem by enabling HAGS. I personally don't have it enabled and everything works, but maybe it will work for you? https://www.pcquest.com/w.dows-10-may-update-hags/

Qaedyn

• AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable --- Confirmed no problem, 4k @ 120, 10bit, G-sync, 4:4:4

So I picked up my CX 48 at Best Buy yesterday and got an AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable have had no issues with my 3090 ftw3. First thing I did was upgrade my firmware to 3.11.25. Any of the AudioQuest 8d-10k listed cables at Best Buy should be fine but anything over Pearl gets expensive quick and you only gain better auto quality apparently.
 
Edit: Woops restrictions on new members and links...sigh. Tried to post links to the cables. Just search for the Pearl or Ocean (apparently same quality as Pearl but BestBuy exclusive) 8k-10k HDMI Cables at BestBuy. Also AudioQuest has their own site as well if you want to see more info on the cables.

 
Thanks for the tip, I may give one of these a try, was looking at the pearl/forest.
 

arestavo

PhantomApollyon
Update: I tried the Monoprice 6ft cable with no change in behavior at all - still having the same issue

I just read that someone else fixed a black screen problem by enabling HAGS. I personally don't have it enabled and everything works, but maybe it will work for you? https://www.pcquest.com/w.dows-10-may-update-hags/

 
I did give that a shot and no change unfortunately.

Update: Turning OFF Windows's fast startup corrected my one outstanding issue with literally no noticeable change to the speed of the machine starting up.
 
System > Power & Sleep > Additional power settings > Choose what the power buttons do > Change settings that are currently unavailable > uncheck "Turn on fast startup (recommended)"

Thanks a lot for this great thread. Following the guide laid out in the first message I was able to get my 3090 FTW Ultra and CX 48 set up with no real problems. It did take a few tries to get Instant Mode to kick in but I am sure it was due to my missing a detail. Love the image quality. 
 
 

I'm using this 25ft fiber cable as my PC is quite a length away from my LG CX 55 @ 120 Hz with HDR on and full RGB and it works fine with my RTX 3090