I've never upgraded to Win10, still running Win7 64bit.
I've got a 970 vid card, but my 1070 will be here shortly. How important will DirectX 12 be for VR, now and in the future? Is it 'safe' to let Win10 update on my Win7 machine? My Win7 machine is my main use computer, and VR.
That's not an issue anymore. Now when you do the upgrade, your Windows key is permanently linked to your motherboard. You can reinstall freely on the same system without ever having to reauthorize your install.
