Low power consumption TRTL mining is a hit or miss thingy and seems to depend very much on silicon lottery.
This can't be the case... I have 8 nitro 64s on a rig pulling 1112w at the wall - maybe ~35w for system, so that's <135w per GPU on average, each doing 18.5 kh/s (850/1107/818/L18+18.) I also have a ref 64 and a flashed ref 56 (850/1107/818/L22+22) doing the same on another rig. These were all bought over a period of many months during the vega stock shortages, so they certainly weren't all binned together.
Granted I'm on platinum PSUs and a 240v line, so your power needs could be slightly higher, but prob not more than 5%-10% max. I'm also on linux, but my tests on windows (18.12.x drivers iirc) showed similar results.
Really, memory manufacturer is the only thing I see impacting performance - mine are all samsung, and i expect based on widespread reports, and my experience w/ polaris, that hynix would underperform. Drivers are the other possibility - though I have yet to see any versions since blockchain significantly impact performance for any algo (other than on xmr-stack derived miners.)
8 nitros 64 pulling only 1112W at the wall is mighty impressive!! I think you might be the only person being able to pull that off
The problem with my rig is none of my Vega64 nor Vega56 cards is able to run at 1200/1100/<880mv/L28+28(L24+24) without crashing. Same goes for CNr algo. Can't go below 870mV. So, I am really baffled how you are able to pull off that power draw. Wonder if temperature have a role in the stability that you are getting with that extreme undervolt. It's hot where I live and my GPU temp is 65C.
The 850 cclock and cn_config=L18+18 are key. IIRC, for the same exact voltage setting, I saw a 15w difference in power consumption just increasing cn_config to L28+28.
I also had a ton of trouble trying to find stable settings for the 1950 h/s range - at the end of the day, the time spent hunting for stable settings, plus the extra power required, just weren't worth the extra 1kh/s.
That being said, if you can't get < 880mv, you likely have a problem somewhere else, possibly your ppt - try disabling all other states, or make sure you don't have out-of-order voltages (since 19.x, many people are forgoing ppts, which is a mistake given that you still can't change the mem-p2 voltage setting.) And while higher temps do require more power, it's also all the more reason to get your voltage down...
