The freesync range of that monitor appears to be 40-144, so if the FPS gets outside of this range, you will get tearing. I suggest running with one card, and seeing if it is a crossfire issue. When it comes to blizzard games, I just turn on vsync because I have found their games do some strange stuff graphically speaking.
Thanks for the reply. My average framerate is usually between 100-120 with crossfire enabled and freesync enabled (no tearing, very smooth, no vsync). Overwatch often has issues with freesync and crossfire flickering. Now the tearing is very bad and it feels pretty off. Driver versions 16.7.X to about 16.8.1 worked the best for me across the games I play with Overwatch working fine. I won't use vsync because the input lag is rough and I paid a good amount for this setup.
Replying in case others had similar issues:
Clean removed 16.10.1 and installed 16.7.3, re-enabled freesync and my system is a lot more stable.
My issue with Overwatch on 16.10.1 MIGHT have been due to the poorly labeled but combined resolution/refresh rate setting, I think I had it on 2560x1440 instead of 2560x1440 (*144). Other games that have proper crossfire support like killing floor 2 had frequently high frame time spikes too on 16.10.1.
Since all is well I don't want to go back and try it though, and I'll stick with this driver for another few driver releases.