Is this only happening in Wildlands or is it happening in other games/benchmarks/stress tests?
In my dad's old system which was a 3930K and a MSI X79 GD45 Plus motherboard, and 2 GTX780Ti's in SLI when he was playing Elite Dangerous he would get issues where the system would crash and lockup, if he disabled SLI it worked fine but as soon as he enabled SLI it did it again.
This would happen in games and benchmarks etc and in the end I took his cards out and put my 980Ti's in it and tested it and it continued to show issues, so I put his cards in my system to try them and they ran fine.
Changed the PSU, Ram, HDD's, SSD everything that we could think off, remounted the cpu and the H100i, checked the socket for bent pins etc and there was none, checked the PCI-E sockets and no damage there.
The only thing that we can think is that one of the PCI-E slots has failed but only when 2 cards are being used as they all work fine on there own with graphics cards in them, or the CPU has started to fail, we both however believe it's the motherboard but as of yet have not been able to test that.
To me the issue in your system could be hardware if it's happening in other programs etc but if it's only in Wildlands then personally I would wipe a hdd and install windows on to it, with drivers and only the required software to be able to play Wildlands and then I would see what happens, if that works flawlessly I would then install other stuff 1 program at a time and retest to see if anything causes it to fail.
One thing I did notice which was weird on my system, is that if I have nVidia Inspector open and then try to play the likes of COD 4, the game will crash after a few minutes or a few hours, but if I close it then they work perfectly, which is why I would do the above with a spare hdd and see what happens.
It will take a while but it might be worth it.
