Volle said:
<Excessive wall of text>
Well, doesn't help me since I don't have a dual boot system with Linux.

But I've done a 4th attempt today.
I uninstalled my antivirus programs (Avira and Malwarebytes)
I uninstalled my Firewall (Comodo Firewall)
I uninstalled the realtek ethernet controller drivers
and I deleted the reg key which was referred to in the last setuperr.log (the key was related to something called Xbox Game Input Protocol Driver

This time, it succeeded! :)
Running Windows 10 1511 now without issues (however intel rapid storage icon doesn't appear anymore on the task bar, nor can I find it back anywhere, but is that much of a concern?)*
Do I have to merge the deleted reg key back in? I checked the registry and the deleted reg key was already present (regenerated by the upgrade?)Thank you Windows Sniper, your advice has worked!

*Edit: Fixed the missing intel RST thingy by installing the missing motherboard driver from the manufacturer's site.