I just got a second ACX 2.0 and I benched them both individually. They seemed stable enough @ 200Mhz core, 500Mhz memory each (linked) - No voltage boost. I run Witcher 3 @ 4k/60Hz. 
 
Every once in a while the screen blanks and then comes back- there's sound and everything like the game is continuing, but it takes a second or two and then the screen comes back on. It didn't seem to do this when I was running on just one 980Ti alone. What's going on here? The cards are stable when I bench them and it didn't happen when I was running one card alone. Is this a driver bug? Is it the game pushing the cards too hard? Did I get a bad second card or something else entirely?
 
Any suggestions would be greatly helpful.

I'll have a bit of headroom too. I haven't really boosted the voltage much so I can fool around with that. I'll probably have to lower the overclock in the end.
 
I'll see what happens if I still have problems on default stock speed.

That problem what people describe as black screen, losing signal, with Maxwell... that happen with all Maxwell cards, and TITAN X or only with GTX980/GTX980Ti...
GOD DECIDE TO INVOLVE HIS FINGERS WHEN NVIDIA START TO CRIPPLE PERFORMANCE OF 10  MONTHS OLD CARDS ONLY TO PEOPLE BUY NEW MODELS. 
 

ericfis

evh19781984
this is the same basic problem i am having on a single  980 classified card and mostly on older games?
it is just like you described the screen goes blank but the sound remains and then after a while it comes back?
I never had this issue with my 780ti superclocked and all my newer games played fine unless the game needed a patch.
 

Yes, that's it exactly. I was running 3 OG Titans in SLI previously and never had this problem. So it's more than just me? 
I'll have to try some other games and see what's up- I've only been playing Witcher 3 exclusively lately, and that clearly pushes my setup pretty hard.

for me it is the older games that really are a problem,titles like modern warfare 2,3 and 4 and the ghost recons 1+2.  
Watch dogs plays flawless???  thats really making me scratch my head?  I thought if any game would have a issue it would be that one, but i played that for several hours and not a single problem?
But on those older games i can only get maybe 5 mins of gameplay then blank screen, and sometimes it comes back but only for a few seconds and then back to black screen.
Obviously the game is not enjoyable this way! LOL
I am thinking of installing my 780ti back in this tower just to see if it still does it on those same games.
got to start narrowing down the "what it could be's"

ericfis
https://www.reddit.com/r/nvidia/comments/383zd1/still_getting_display_driver_crashes_during_the/
 
It appears there are lots of people with 9xx series of cards having this problem. Some possible solutions there. I'll test some of them out and post back.

yeah all we can do is try them one by one until you find a fix
I dont even know if all of us are having the same exact issue but nonetheless
there is something up with the 900's.
I even tried putting phys x on cpu in my NVCP to see if that helps.
A few guys did that and said it worked.