I've seen claims of decent speed improvements when using CachyOS, though I can't say I've ever hunted down solid confirmation. I'm a bit wary of the project because I would have to put a lot of trust in them since they're rebuilding everything themselves and could easily introduce malware somewhere in there. (But I've been scared of distros before only to have it pointed out to me that some very well respected people are involved, so I could be worrying for nothing here too)

Does Gentoo have binpkgs with these compileflags? With CachyOS you don't have to compile, because it's a rolling binary distro. Regarding your [1]: They do that, systemd(or parts of it) are unoptimized, for instance. They don't apply that stuff blindly, only where it works.

For me it feels blazingly fast, even on obsolete KabyLake Core-I5/7(t) forcibly clocked down to about 800Mhz most of the times :)

It fucking flies without much effort. On modern systems even more so. While being rock solid. Without any crashes. Even under Plasma. When I'm reading about bugfixes regarding crashes under Plasma I just shrug and think "Waddya talkin about?". That may be hardware dependent, though, because they are old Lenovo Thinkcentres(1Litre SFF M910q tiny) with excellent firmware.

Using btrfs, profile-sync-demon, zram(Yes. Even with 32GB Ram!). Suspend/Resume working every single time. No glitches, hick-ups, ever. So far. Since 10th of June, 2024.

Edit: Almost always some music out of yt doodling in some bg-tab, in oh-so-slow FF, without any clicks, stuttering, or other breaks.

No need for yt-dlp, mpv at all. Except for dl/saving stuff, sometimes. While FF is rarely under 100 tabs.