Yes they're both fine on their own.
At the moment I've tried increasing the voltage on my cpu even though it''s not overclocked because I found a post on another forum where someone had the same problem with sli and increasing the cpu voltage worked. I think it's helping but it hasn't been long enough to say it's fixed it.
EDIT: (FIXED)
I've managed to have crash free gaming for a few months. I reduced the clock speed on the card with the higher boost to match the lower one and set the power management mode to "prefer maxiumum performance" in the 3d settings of the nvidia control panel.
I hadn't bothered to match the clock speeds before because they usually automatically boosted to the same speed but I noticed than in Doom they were running at different speeds.
I haven't tried a lot of games but it has worked for Overwatch, the Witcher 3 and the Divison.
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