The last few updates have had a range of complaints from issues regarding performance hits to freesync having issues and similar to your issue as people have said it is making their GPU unstable and causing it to crash their system. Perhaps this could be the same problem you are having?
Have you tried installing an older driver to eliminate the driver being an issue?
The stock cooler should be able to do minor OC but if you want to go for 4ghz + then maybe a hyper 212 evo? its about 5 pounds more than the cooler listed in your link. Other than that it looks solid and should do the job.
On Ryzens launch Overwatch seemed to have an issue with it as on their forums there are posts of problems similar to yours. It could be the game isn't optimized for Ryzens architecture and in turn is taking a performance hit.
When Ryzen 3 launches that percentage might increase given rumors of it being priced between i3 and i5 but delivering i5 performance.
Interesting to see none the less.
I have seen may people achieve 3.8ghz with ease so this video should help. Also includes a good note on not to mess with the fan profiles in the bios since with that MSI board it causes major issues