In my testing on a similar hardware (also Core M3 and 4gb RAM), Arch-based distros was the best with low RAM. And I tried like, probably 50 distros since last year...
Gnome on my HW with Arch, is as fast as KDE, and use less memory than KDE (in theory, I know RAM is a complicated subject).
Why fedora is problematic on low end hardware? Because well, Fedora uses packagekit, which is a ram hog, and this is pretty known. Is not the only reason though, I believe there's some other defaults that make it slower than arch on my HW, like zswap vs zram.
In my experience with weak CPU and low ram, was that zswap was actually the best choice. On such low RAM like 4gb, you'll really need a swap, you can't run from this. And zram won't be enough, in my experience.
Which I guess is one of the reasons why Arch go very well here, as is one of the few distros right now that does a nice default for zswap.
With Fedora, and most other distros, I get constant freezes when the RAM is full (which is pretty easy to do with 4gb), and this never happen on arch based distros.