I also have a 2080 Super and it is stable at 900 mV, I tired 875 but wasn't stable. I would try that 2080Ti at 900 mV.That undervolt is way too low for a 2080ti IMO. My 2080 Super has an undervolt of 919 mV and I found this to be stable in everything I do, and I can't go any lower. Of course, undervolts are like overclocks, in the way that each card is different, but most of the 20 series undervolts I've seen are usually above 900 mV