Gnome 3 runs like an absolute dog on my Skylake notebook using Ubuntu 19.10. I don't know what metrics you have been looking at, but as a regular user I "feel" that the UI is constantly lagging during regular use. I didn't think it was this bad when I was using Fedora in the past, but that was a wayland based installation.
Weird. I'm on a ThinkPad x230 Ivy Bridge and Gnome (3.36) is butter smooth for me (Ubuntu 20.04, fresh install). I did the minimal installation though.
Enabling the BFQ scheduler reportedly boosted the responsiveness https://bugzilla.redhat.com/show_bug.cgi?id=1738828 and I can't remember where I saw someone saying it had a positive impact on Gnome in particular.
