Windows 8.1 was my last version before I made the switch. Windows 8 was horrible. The Metro UI broke all my habits from Windows XP from 7 while also making it harder to tweak my system. By the time 8.1 came out, I'd found enough ways around the main annoyances that its improvements were moot, but many issues remained, such as the bloatware bundled with my PC, and frequent slowness and instability.
As for why I switched, I was attracted by the free software ideal, and trying to get away from Windows, and I had watched and read several things that further convinced me it was superior, but I think the ultimate reason was that I had become hyperfixated on Linux. Thankfully, in this case, autism did not steer me wrong. My level of obsession with Linux has declined, but I still enjoy using my computer much more than I ever did or would on Windows.
I don't have much PC building experience, but these specs seem sufficient. Only comment is that you might need to use a distro with a new-ish kernel and graphics stack, given the very recent CPU and GPU. So not Debian stable, but Fedora, Ubuntu, or any rolling release distro will be fine.