For kicks, I decided to test LXDE on Zorin OS 16.
It was one of many I tested out today, but the only one that really stood out and performed very well.
This one was a lesson in my preconceptions... I had low hopes for it. Yet, LXDE was very pleasant and snappy. Openbox WM left something to be desired, as did the App Menu. But aside from that, all apps worked properly, for the most part. The only app that did not was the obconf. It liked to freeze and stay that way, unusable and could not close it, either. Had to kill it.
I then tested the LXDE-gtk3 port. It ran at the same performance and speed as LXDE, integrated as well with all themes as LXDE did - but included updated apps including obconf that did not crash but worked perfectly. On top of this, the applications had more settings and more ease of use.
I then replaced the Openbox WM with what I already have installed: XFWM4. This allowed my normal window borders. It is easy to also just run an instance of XFCE4-panel with Whiskermenu rather than the LXPanel with very basic app menu.
The speed and performance remained the same doing this as well.
LXDE is a surprisingly configurable and well developed desktop. I have the feeling I will be exploring it again on older notebooks.
It is definitely a desktop environment that is worthy of attention and consideration. Most any setting or configuration is readily available.
That being said... Its speed and performance were on par with XFCE4, which offers more features, a better window manager, better App Menu and much more in the way of Panel Applets.
Given a choice between the two, I would go with XFCE as it has more current support and more to offer while still being as lightweight.
At least for as long as XFCE retains its Window Manager and doesn't continue its path toward being a lightweight Gnome-clone that is.
LXDE is more than just noteworthy and has just made my short list of Potential Desktops to replace XFCE or Cinnamon should they go South (And one of the two has chosen to go in that direction).