Wow! I'm having a similar problem as you! Been reporting to Sapphire and AMD without response. But my card crashes on both Win8.1 and Win10, fullscreen or windowed, and its not OC by me but from Sapphire. Driver 16.2.1 work perfect on both OSes. Also, my display doesnt have freesync. My Sapphire R9 285 Dual-X OC is constantly crashing, and thanks to you I found that the only driver that DO NOT CRASH is 16.2.1. I'm on Win 10 x64 up to date. To add more info, when the card crashes, I cant recover and have to hard-reset the CPU. This is terrible and this didnt happen on Win8.1. So I went for it and installed Win8.1 x64 on a new hard drive, installed 16.5.1, Dark Souls 3 and it crashed in 5 minutes of gameplay! But I could open task manager, kill the process, and try again. Used DDU, installed 16.2.1, all worked ok... Sigh. So all in all, I think the card work ok, AMD drivers sucks real bad, Win10 do not play well with AMD drivers, and the only solution for me now is to use 16.2.1, which of course is far from ideal as I miss fixes that are on newer drivers (fixes for Quantum Break, Hitman, Fallout 3 and even Dark Souls 3).