I upgraded to Windows 10 Anniversary for Halo the other day, and it ballsed my Overwatch right up, my FPS was down to around 100 ish which renders my 144hz monitor a bit useless.
So here's what I did to fix it!
The grraphics preset was set to 'Low' on Overwatch, but when I expanded it just about every setting was on Ultra. So get rid of those tasty pixels and get back onto low, set your render distance to around 70% if you're struggling to get the FPS.
Check your mouse profile, mine got reset so I was playing on double the DPI I usually do, which explains why my Mcree was so bad.
Go to the Xbox app, go to settings, DVR Recording and disable that, I noticed a minor FPS increase after doing that.
Finally, I got rid of Cortanna using the .reg 1 click tools found on this guide: http://www.howtogeek.com/265027/how-to-disable-cortana-in-windows-10/ but that's purely because I didn't really want Cortana, I didn't notice any increase in performance after removing this.