I had success with a Dell Latitude ST with a Z670 Atom processor moving from 8.1 to the Windows 10 upgrade using USB installation media created with Microsoft's USB/ISO tool. No failed test, just took a lot of time.
I downloaded the tool from there, used the tool to download the universal 32/64-bit ISO (you can't leave it on auto for that) and extracted the ISO using WinRAR to a folder on my Windows 7 32/64-bit installer USB drive. I used it three times in the past week to upgrade PCs to Windows 10. I figure it's best to get in before the upgrade deadline.