Why am I unable to properly use late 2015 / 2016 drivers?

I always use DDU, without even touching AMD's uninstaller.

 

DDU is the best!

 

Improper overclocking probably causes most crashes tbh, at least in specific circumstances such as yours. This goes for both graphics cards and the computer in general. I've seen computers pass stress tests, yet crash in games etc, and all that is required is lowering the overclock. In your case it's probably because the later drivers make better use of the video card and happen upon the instability caused by the overclock. For crashes caused by general overclocking, it's possible it's related to having a variable load versus a fixed, albeit heavy load in stress testing.