Last night I installed Enterprise versions of 8.1 and 10 into an empty partition on my machine and dual-booted into them just to see what it was like.
8.1 was trash, it didn't last very long before being wiped. Interface complaints aside, while it was usable even with the exact same video driver as with my win 7 install it wasn't an improvement. The backlight on 7 appeared to be more stable. Also ran into an issue where dual boot trashed my ability to log back into 7, freezing at classpnp.sys. I eventually figured out I needed to turn legacy boot back on in the bios. After that, dual boot worked fine. It was probably working fine before with legacy off because I had grub as the bootloader which has full uefi support. There was one good thing about 8.1 though. Due to its more up to date driver infrastructure it was able to show me that my USB enclosure/drive isn't defective. I couldn't understand why in 7 writes were 2x as fast as reads over USB 3. It's some kind of software issue because in 8.1 reads were full speed.
Next, I tried 10. Since I had never tried 10 on my machine before I needed a baseline to refer against especially in light of the 2004 thread so I installed 1507. My interest in doing so was I had remembered Gurm saying he thought it might even be better than 7 and a fair few other people here liked 1511 fine.
It booted up into the MS Basic Display Adapter and I was quite surprised by how stable the image looked. Unfortunately due to the auto-update nature of 10 it means that I need to repeat it without a network connection with auto-updates disabled in order to give me a moment to really look at it with that adapter (will need to disable auto-updates in the settings).
While looking at it in basic it suddenly snapped in a Intel driver from 2016. Image slightly worse but not bad. Right-clicked and had it search for more, it located a 2017 dated driver. Not worse. At this point I figured since it was a touch unstable having experienced at least one crash opening a folder and wanting to test basic mode more, prior to that I decided to download and install the latest driver version from Intel's site, reported as wddm 2.0 in dxdiag.
Much to my surprise the latest version was better. Even though the image seemed duller/less saturated with a different white point (might be an auto-installed colour profile) it was presenting a picture that appeared smoother and didn't have as much of that shimmer which I was seeing in 7.
Conclusion, interface and other complaints aside like blurry fonts due to dpi virtualization, 1507 on my hardware appears at first glance to be less tiring than 7 which is already the baseline I measure against. I will need to spend more time with it but I am pleasantly surprised as it's nice to test a still supported OS with the latest Intel driver (ltsb 2015 receives security updates until 2025). I think I will also take a look at 2004 as well though I tend to not like rolling software updates which introduce bugs and instability that Windows 10 is notorious for.
On a future date I'll play around with other OSes on this machine too (BSD, Linux) possibly including MacOS as well though that one I might try just on the external drive.
@tfouto since we have the same hardware and bios other than the cpu, you should consider dual booting your 8.1 install. It's easy enough, free up 33 gigs of space, and do a custom install (not upgrade) to the empty partition space created.