This is based on a youtube video where RAM and disk usage of different Ubuntu flavours were tested. (See it here (https://www.youtube.com/watch?v=dyNVpWyVP-M). I was somewhat surprised at the RAM results, which I captured with a screenshot (posted). I know that Gnome would be heavy on RAM, but I was surprised by how much more RAM it used than KDE Plasma (1.3 GB vs 460 MB). Budgie was almost double KDE, but it is based on Gnome. The lowest usage by far was LXDE (260 MB). I don't know how much that matters when you have more than 4 GB of RAM installed. With sufficient RAM, does lower usage necessarily mean a more responsive system?
Note that the really low usage window managers like openbox and enlightenment weren't tested. I know from experience that openbox is much more nimble than Gnome, even with lows of available RAM.
Fascinating!
I'm surprised that Kubuntu uses even less RAM than Ubuntu MATE. As to if lower RAM usage means a more responsive system, that's hard to say. My gut feeling is that unless you're using over 75% of available RAM, probably not. If you're using programs that consume a lot of RAM then having more RAM available will help with the response time of the OS overall if it puts you over that (image editing, video editing, 3D work, maybe heavy scientific apps).
However, it should affect load-time since all that data has to be read off off the hard drive to put in RAM so you get to a desktop. I don't know how much of the desktop RAM that is used is dynamically-used. If a good portion of it is, then that would mean that the CPU has to re-cache it for updating things so larger desktop memory use could result in slower response though I'm not sure how noticable it would be since RAM is so fast (in human terms).
In my case, running out of RAM is highly unlikely since I have 16 GB in both my home and office computers.
Not likely in your case if I understand your usage. But make no mistake, there are applications where even 16 GB of RAM may not be enough, and when I use applications here, I don't mean software applications, I just mean certain uses.