I'm using KDE on a System76 Lemur, and it's snappy. It's also not a twelve-year old Thinkpad like my previous computer, for which KDE was not appropriate, but KDE is lighter relative to current hardware than it was eight or ten years ago, when I last used it in earnest on a machine that made sense. I never expected to use KDE again after my experience back then, but they've made it perform well while doing everything I could want a DE to do.