From the outset, I'd just say I don't get my systems in a state - no 3rd party AVs, no Customised Start menu, no registry cleaners etc. I might have 7-Zip and EasyBCD and Macrium, and run a modified hosts file, use Chrome Canary, and restore Windows Photo viewer, but little else.
I have one older laptop that runs Windows 10 fine, with the exception that it won't upgrade, and won't clean install due to lack of OEM drivers and something about Windows 10 setup on that laptop that causes the hardware to be assigned conflicting IRQs. I think it is to do with WinPE during setup and lack of Chipset drivers.
How do I know it can run Windows 10 then?
Initially the laptop was running XP and Windows 7 Ultimate in dual boot.
The Windows 7 failed to upgrade to 1507, so I left it for a few months and tried 1511, which caused a Frankenstein's horror of a protracted overnight installation and then problems with setting up a user because it was running sooo slowly due to the above IRQ assignment problems. Eventually, and extremely slowly, I disabled some hardware in device manager and the system ran, but with the defaultuser0 profile as the main user, and no administrator access, I returned it to Windows 7 from a backup. It had however, I discovered later, assigned a digital licence to the laptop.
Then I discovered the laptop runs a portable Windows 10 Pro as a Windows to Go installation on a USB drive, so it is not the hardware that is a problem, at least as far as running Windows 10 is concerned.
If I use the same logic as a Windows to Go installation, if I avoid Setup, and apply the Windows image to a clean partition on the hard drive from install.wim (or install.esd) using DISM or preferably Imagex, Windows 10 completes the OOBE, I can set up a user, find some older drivers for the chipset and more esoteric hardware, and adjust the basic graphics driver to get a reasonable result on the unsupported Intel integrated graphics.
The next thing to try is to transfer the disk image of this to another machine, upgrade the OS build to the latest Feature update, and transfer it back to the laptop, having wiped the old system off.