1. The stuttering could have many causes - the most common of which is simply a buggy 'upgrade' process. Once upgraded to W10, a clean install (skipping any request for a key) should've fixed that.
2. Is the Assistive Tech upgrade still working? It was going to be pulled, due to abuse. It was meant solely for those who require those assisted tech programs.
If I understand correctly, you've already upgraded on your current hardware - therefore, you don't need to 'upgrade' again (provided your copy of W10N was 'activated'). You can clean install W10, provided you use the correct copy - and it'll just reactivate.... on current hardware.
You can download/create media here:
https://www.microsoft.com/en-ca/software-download/windows10
When installing, just skip when you're asked for a key - your hardware had a ID assigned, and will be recognized once you're online.
As for moving to a new Kaby Lake build - officially, it's a bit of an unknown.
Technically, you can now make 'significant hardware changes' (including MB*) and still reactivate - provided you've linked your W10 install to a MS account.
https://support.microsoft.com/en-ca/help/20530/windows-10-reactivating-after-hardware-change
*Now, whether a whole new build with Kaby Lake is a 'significant hardware change' or an entirely new system is somewhat debatable.
For your best chance of success on your new build, you'll need to reinstall W10 on your current setup, and follow the instructions linked to tie it to your MS account. Then, build your new system - and I would recommend a further clean install at this point, then follow the troubleshooter if it doesn't simply 'activate'.
There's no guarantee you can move it over (again, signigficant hardware change vs new build debate), but that would give you the best chance of success.
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