I only have one card for mining. 
Second card is just for Windows and gaming.
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.