Ainars what motherboard / CPU do you have in your AMD rig please? I tried the Vega on a couple of boards with Windows 7 and they both bluescreen trying to load the driver. Put 10 on one of them and it did exactly the same. They all run the GTX960 just fine. I've not tried 8 since the blockchain driver is either 7 or 10.
I'm wondering now if my 'spare' kit is just too old for cards like this
The first one I tried them in is a 1st Gen i7 though, which is still a decent machine.