Looking at the pages for test 3 while you were still mining, the vardiff was actually using ccminer and d=10 coolminer according to the pool (or the other way around, don't remember which). Didn't say anything as I was unsure if that was intentional.
I only have one card for mining. Second card is just for Windows and gaming.
then 12gb should be enough. Old driver? upgrade to the latest
Yeah, I'm using 391.24 from 2018.3.20. Friend literally updated minutes ago and his machine became completely unstable so I guess there's still some instability with the 397 drivers. Might give them a try later.